What does the term "soul sleep" supposed to mean, exactly? It seems to address several different but related concepts: whether the soul continues to exist after death (mortalism), whether the soul has a conscious existence in the postmortem state and if so to what extent, whether the soul is not merely conscious but active, and so on. The Society confuses things somewhat, such construing a statement that the "dead are conscious of nothing at all" (Ecclesiastes 9:5 NWT) as proving that death is non-existence.
It is crucial to understand that there were a variety of beliefs in early Judaism and Christianity which developed over time, and the Bible samples a portion of these. It is thus artificial to construct a single doctrine as the "true Bible teaching" on the subject. When we look at the Bible in its literary and intellectual context and example the range of ideas in early Judaism, we can see that there was indeed one sect that believed that the soul perishes at death: the Sadducees. Their non-belief in the afterlife was directly connected with their non-belief in resurrection, for central to the latter doctrine is the idea that a person who dies will arise and live again. The Sadducees left no books but their ideas are widely represented in early sources. Hippolytus wrote that "they deny that there is a resurrection, not only of flesh, but they also suppose that the soul does not endure (psukhén mé diamenein)" It is only the life, and it is on acount of this that man has been created. However the idea of resurrection is fulfilled in this: in dying and leaving behind children upon the earth. But after death one expects to suffer nothing, either good or bad. For there will be a dissolution both of soul and body (lusin kai psukhès kai sòmatos), and man passes into non-existence (eis to mè einai khòrein), similarly also with the members of the animal kingdom" (Adversus Haereses 9.29). This contrasts with the views of the Essenes and Pharisees, who believe "the flesh will rise again (tèn sarka anastèsesthai)" and there will be a "resurrection of flesh (sarkos anastasin), and the righteous will be "imperishable" (aphthartous), as "the soul is already immortal" (èdè athanatos estin hè psukhè). Similar statements about the Sadducees occur in Josephus who says that they teach that "souls perish together with bodies" (tas phukhas sunaphanizei tois sòmasi) and reject the idea of "the survival of the soul" (phukhès tèn diamonèn) (Bellum Judaicum 2.165, Antiquitates 18.16). The NT also presents the Sadducees as believing that "there is no resurrection" (Mark 12:18, Luke 20:27, Acts 23:8), and Luke specifically criticizes in a parable the Sadducee belief that there is no postmortem punishment and resurrection (16:19-21). The Sadducee belief was probably the heir to the perspective in Ecclesiastes, which not only claims that the dead have no reward or conscious thought but that they would not ever return to life: "The dead know nothing, they have no further reward....Never again will they have a part in anything that happens under the sun" (9:5-6). The Watchtower teaching seems to make an uncomfortable compromise between the Sadducean annihilationist belief and the Pharisee/Essene/Christian belief in the postmortem state: The dead are non-existent but they will also be resurrected to life by copying and recreating their "life patterns". This is distinct from the actual Jewish-Christian concept of resurrection which always presumes some continuity between the person who died and the person who is raised.
The Sadducees in rejecting the idea of resurrection were religious conservatives, since resurrection and eschatological judgment are concepts that the Jews adopted in the post-exilic era, possibly from Zoroastrianism. Their idea of death also eschewed the influence of Platonism that deeply permeated Jewish thought in the Hellenistic period. But it wasn't immune from Greek influence: the idea of "non-existence" at death goes beyond what was believed in pre-exilic times (as well as what is found in the post-exilic Ecclesiastes) and may represent influence from Epicureanism (Sadducee ethics also resembles Epicurean views in other ways). The Israelite perspective on death was very close to what was earlier attested in Canaanite religion: the dead have a shadowy existence in Sheol similar to sleep but which may be "roused" by the living. The postmortem denizens of Sheol are called r e pha'im in the OT — a word that is cognate to the Canaanite word for the same thing, rp`um. The rp`um reside in the underworld, they include all the ancient warriors and kings of the past assembled together, and they may be invoked in blessings as 'ilm "gods" (KTU 1.6 VI 1-6;1.15 III 2-4, 13-15; KTU 1.20 I 1-3, II 7-9; 1.22 II 25-27, I 10-25; KTU 1.161 R 2-26). They are also mentioned in sarcophagus inscriptions of Phoenician kings, warning grave robbers that they would have "no offspring among the living under the sun nor a resting place among the rp`um" (Sarcophagus Inscription of Tabnit, king of Sidon, lines 3-8; Sarcophagus Inscription of Eshmunazor, king of Sidon, lines 4-12). The OT references to the r e pha'im are part of the same intellectual tradition. When the king of Babylon descends to Sheol, Yahweh rouses (`ôrer) "the r e pha'im of all of the rulers" (r e pha'im kal-`âttûdê) and makes all the kings of the nations "get up" (hêqim) from their thrones, such that Sheol is "astir" (ragezah) to greet (liqrâth) the king's arrival, and the r e pha'im will each say (w e yo'm e rû) to him: "So you too have become weak like us, you too have become like us" (Isaiah 14:9-15). In Sheol, "the r e pha'im tremble (ha-r e pha'im yechôlalû)" before Yahweh (Job 26:5-6) and all who sleep in the ground will feast ('akelû) and worship him and kneel (yikr e `u) before him (Psalm 22:28-29). The r e pha'im are viewed negatively in Proverbs as residing "in the depths of Sheol" and the man who strays from righteousness will rest (yanûa ch) in the "assembly of the r e pha'im (biqhal r e pha'im)" (2:17-18, 9:18, 21:16). The prophet Ezekiel also envisions activity in Sheol. The armies of Egypt and their enemies both go down into Sheol uncircumcised and the "leaders of the mighty warriors" ('elê gibbôrîm) inside Sheol notice that those fallen (nophelîm, cf. the gibbôrîm in Genesis 6 called the N e philîm) by the sword "provide a bed" (nat e nû mishkab) for the newly slain to recline on (hashk e bah) and rest (shak e bû) while "bearing their shame (wayyis'û k e limmatam)" (32:18-25).
So as denizens of Sheol, the dead sleep until they are roused, they tremble before God and kneal before him, they experience distress and bear their shame, they talk to each other, and they form an assembly and greet newcomers. The dead bear some resemblance with the people they were in life: the dead kings in Isaiah 14 still sit on thrones in Sheol, the slain Egyptians and Gentiles still maintain their circumcision status in Sheol, and in the En-Dor story Saul recognized Samuel from the mantle he used to wear (1 Samuel 28). The Society claims that the spirit called up by the necromancer was a demon, but the story only makes sense if the spirit was really Samuel. He speaks with the authority of a prophet of Yahweh (v. 16-17), as Yahweh's representative he explains to Saul the reason why Yahweh has not responded to his prayers (v. 18), and Samuel makes a true prophecy of Saul's imminent doom (v. 19). In no sense does the author qualify the references to Samuel. "Immediately Saul fell flat on the ground, filled with fear because of Samuel's words" (v. 20); the spirit that appeared was indeed Samuel for the author. Samuel was described in 1 Samuel 28:13-15 as ascending up from the ground after he was stirred (hirgaztanî); this is the same verb that occurs in Isaiah 14 to refer to the r e pha'im of Sheol being made "astir" (ragezah). Samuel is also called an 'elohîm "god" and this word is elsewhere used to refer to the dead in Numbers 25:2 (cf. Psalm 106:28) and Isaiah 8:19; cf. the rp`um in Canaanite texts being called 'ilm "gods". The later version of the story in 1 Chronicles 10:13 also implies that the roused Samuel was an 'ob (cf. Arabic 'awaba "a spirit that returns [from the underworld]") and this is the word used in Isaiah 8:19, 29:4 to refer to the spirits of the dead called up by mediums. The polemic in Isaiah 8 (with parallels to the law against necromancy in Deuteronomy 18:9-11, cf. also Isaiah 65:4) was not that spirits of the dead do not exist and cannot communicate with the living but that Yahweh forbids his people to consult them and obtain prophecy from any other source than his prophets. But while the Deuteronomistic law forbade necromancy (which was not banned in the older JE law code), giving food to the dead was not. The tithe stipulation in Deuteronomy 26:14 presupposes that food was indeed "given to a dead person" in ancient Israel and does not prohibit it; it only forbids any use of such food in the tithe. Since uncleanness was mentioned in the preceding clause as making tithes unacceptable, the prohibition probably had in view the uncleanness resulting from contact with the dead. The tacit permission of the feeding the dead (except in connection with tithing) thus indicates again that the dead were normally viewed as having some sort of afterlife existence. Telling too is Tobias' advice on the feeding of the dead in Tobit (fourth century BC): "Be generous with bread and wine on the graves of virtuous men but not for the sinner" (4:17). Another example of a biblical character possibly experiencing an afterlife is Rachel, the wife of the patriarch Jacob who was the mother of Joseph and Benjamin. The prophet Jeremiah was informed by Yahweh that Rachel was heard in the Benjaminite city of Ramah as mourning the capture and exiling of her descendents following the destruction of Jerusalem in 587 BC (Jeremiah 31:15). There is a related tradition in the midrash that Jacob buried Rachel on the road from Ramah so that Jews would pass her grave as they were taken in captivity to Babylon and she would be able to pray for them (Pesikta Rabbati, 3, 83).
When we encounter more elaborated eschatological schemes in the post-exilic Hellenistic period, there is still a conception of activity and consciousness in Sheol. In the Book of Watchers (third century BC), Enoch is shown hollow spaces inside the earth where "the spirits of the souls of the dead" (ta pneumata tòn psukhòn tòn nekròn) are gathered to await their judgment, where the wicked and the righteous are separated from each other. Enoch then noticed "the spirit of a dead man" (anthròpous nekrous) who "cried and made suit and whose lamentation went up to heaven", and when Enoch asked who that spirit was, he was told: "This is the spirit that went forth from Abel (touto to pneuma estin to exelthon apo Abel), whom Cain his brother murdered. And Abel makes accusation against him until his seed perishes from the face of the earth" (1 Enoch 22:2-12). Then in the Epistle of Enoch (mid-second century BC), the wicked are warned that "your souls will be led down to Sheol and there they will be in great distress and in darkness and in a snare and in a flaming fire" (1 Enoch 100:9, 103:7-8). A similar conception can be found in the Community Rule (late second century BC):
"The judgment of all who walk in such [wicked] ways will bring an abundance of afflictions (lrwb ngw`ym) at the hands of the angels of perdition (m'lky chbl), for eternal damnation (lshcht 'wlmym) in the wrath of God's furious vengeance, with terror and shame without end (lz`wtntsch wchrpt), with a humiliating destruction by fire in the darkness (`m klmt klh b-'sh mchshkym). For all eternity (qtsyhm), generation by generation (ldwrwtm), they will spend in bitter weeping (b-'bl) and harsh evils (ygwn wr`t) in dark abysses (b-hwywt chwshd) without any remnant nor rescue from destruction" (1QS 4:11-14)
This is parallel to the conception of Gehenna and postmortem punishment in the gospels (cf. Matthew 8:11-12, 13:41-43, 18:8-9, 25:31-32, 41, 46, Luke 16:22-24, 28), and Josephus made reference to the punishments of Hades (Bellum Judaicum 2.163; Antiquitates 18.16), as well as the postmortem existence of the righteous prior to resurrection: "Those who exit from life in accordance with the law of nature and repay the obligation received from God, when the one who has given it chooses to receive it, theirs is eternal fame, their houses and families secured, their souls remain pure and obedient, having been allotted by God the holiest region of heaven, from which at the revolution of the ages they return again to inhabit undefiled bodies. But as for those whose hands have raged against themselves, darker Hades receives their souls and God, their father, visits upon their posterity the outrageous pride of their fathers" (Bellum Judaicum 3.374-376). According to the Thanksgiving Hymns, the righteous dead have a blessed post-mortem existence in heaven, who "enter into fellowship with the congregation of the children of heaven" (1QH 3:21-22). Joseph and Asenath 15:7 refers to "a place of rest in the heavens" (cf. 8:11, 22:13), the Greek Life of Adam and Eve describe Adam's soul as taken up to paradise in "third heaven" upon his burial (37:5, 40:1), and the Book of Parables mentions a "treasury of souls ... with the holy angels ... underneath the wings of the Lord of Spirits" in "the ultimate ends of the heavens" (1 Enoch 39:3-7). The Testament of Abraham refers to the "tents of my righteous ones and the mansions of my holy ones" in the "bosom" of Abraham in heavenly Paradise, where the patriarchs ascended after death (20:14), which anticipates the Lukan mention of the "bosom of Abraham" as the abode of the pious Lazarus in his postmortem existence. And so the patriarchs welcome the souls of the righteous: "Great is the struggle of the soul and the danger of eternal torment lying before those who transgress the commandment of God. Therefore let us put on the full armor of self-control which is divine reason. For if we die, Abraham and Isaac and Jacob will wecome us and all the fathers will praise us" (4 Maccabees 10:4; written in the first century AD). Paul, who fervently believed in a future resurrection, also expected to go to heaven immediately after death (2 Corinthians 5:2-9, Philippians 1:23-25), although he seems to regard heaven as the abode of the resurrected faithful as opposed to the earth (cf. 1 Thessalonians 4:15-17, 2 Corinthians 5:1, Philippians 3:20-21). The anonymous epistle to the Hebrews also posited that heaven was the future home of angels, Christians, and the faithful Hebrews of old (3:1, 11:10, 16, 12:22-23). In the NT, the clearest reference to psukhèas a soul of a dead person is at Revelation 6:9-11:
Revelation 6:9-11: "When he opened the fifth seal, I saw under the altar (i.e. in heaven) the souls of those who had been slain (psukhas tòn esphagmenòn) because of the word of God and the testimony they had maintained. They called out in a loud voice, 'How long, Sovereign Lord, holy and true, until you judge the inhabitants of the earth and avenge our blood?' Then each of them was given a white robe, and they were told to wait a little longer, until the number of their fellow servants and brothers who were to be killed as they had been was completed".
That these souls were waiting for vengeance means that they were in the intermediate state between martyrdom and resurrection; the full number is then gathered in heaven as "an innumerable great crowd" (7:9-10, 19:1-2), who have perished in the "great tribulation" (cf. 13:7, 15-17), and their deaths are then avenged in 19:11-21, 20:1-3 when all those who persecuted the Christians perish and are imprisoned. Their resurrection is related later in ch. 20: "I saw the souls of those who were beheaded (psukhas tòn pepelekismenòn) for the witness of Jesus and for the word of God ... and they came to life (ezèsan) and reigned with Christ for a thousand years" (20:4). There is also a strikingly similar description of the dead awaiting their resurrection in 4 Ezra (late first century AD): "Did not the souls of the righteous in their chambers ask about these matters saying, 'How long are we to remain here? And when will come the harvest of our reward?' And Jeremiel the archangel answered them and said, 'When the number of those like yourselves is completed' " (4:35-36).
Paul seems to also refer to the intermediate postmortem state of the dead between death and resurrection, although he does not use pneuma or psukhè to refer to what remains of a person after death. In 2 Corinthians 5:1, Paul refers to the body as "our earthly tabernacle dwelling (hè epigeios hèmòn oikia tou skènous)" and a few verses later states that "when we are in this tabernacle (hoi ontes en tò skènei), we groan out of being burdened (stenazomen baroumenoi), not because we wish to be unclothed (ekdusasthai) but to be clothed (ependusasthai) such that life would swallow up mortality" (v. 4). Paul does not use psukhè "soul" to refer to the internal essence but he does presume that there is an "I" (and collectively a "we" among his readership) that lives within the tabernacle of the body and that the body "clothes" -- and oppresses -- this internal person. Paul also used the clothing metaphor in 1 Corinthians; in the resurrection, "what is corruptible must put on (endusasthai) incorruption" (15:53), "mortality must put on immortality (endusètai tèn athanasian)" (v. 54). This is explicit dualism -- the real person is contained and housed within the body. The author of 2 Peter mixes the clothing and housing metaphors as well, claiming that he was writing "while I am in this tabernacle (eimi en toutò tò skènòmati) ... knowing that shortly I must put off my tabernacle (apothesis tou skènòmatos mou)", i.e. death was shortly at hand (1:13-14). Like Paul, the author here is picturing himself as the "I" housed and clothed by the tabernacle of his body. When Paul refers to his future death, he conceptualizes it as a departure of himself from his body into the presence of Christ:
2 Corinthians 5:2-3, 6-8: "We long to be clothed with our heavenly dwelling (to oik ètèrion hèmòn to ex ouranou ependudasthai) because when we are clothed, we will not be found naked (gumnoi)....But we are always confident and know that as long as we are at home in the body (endèmountes en tò sòmati) we are away from the Lord (ekèmoumen apo tou kuriou). We live by faith, not by sight. We are confident, I say, and would prefer to be away from the body (ekdèmèsai ek tou sòmatos) and at home with the Lord (endèmèsai pros ton kurios)".
Philippians 1:22-23: "If I am to go on living in flesh (to zèn en sarki), this will mean fruitful labor for me. Yet what shall I choose? I do not know! I am torn between the two: I desire to depart and be with Christ (ekhòn eis to analusai kai sun khristò einai), which is better by far, but it is more necessary for you that I remain in the flesh (epimeneinen tè sarki)".
Since the person is "away from the Lord" while in the body but "with the Lord" once he is out of the body, this text suggests that a Christian goes to be with Christ at death. The text however is somewhat unclear whether one is "clothed with our heavenly dwelling" immediately at death or whether this waits until the resurrection; the reference to one being found "naked" (gumnos) may point to the latter. One also does not have to be dead to be "outside of the body (ektos tou sòmatos)" as 2 Corinthians 12:2 suggests; one can depart from the body during a revelatory vision. The same concept appears in Philo of Alexandria who says that Moses was "made incorporeal (asòmaton genomenon) in order to hear the heavenly music on Mount Sinai when he was in God's presence (De Somniis, 1.36). More to the point, the Ascension of Isaiah (second century AD) describes the prophet Isaiah receiving a vision and "he was taken by a trance and his mind was taken from this world (èrthè ho dialogismos autou apo tou kosmou toutou)", whereupon he ascended the seven heavens and witnessed the glories of the divine presence; he was not dead however because "breath was still in him" (6:10-13). Then "his soul returned into his body (epestrepsen hè psukhè autou en tò sòmati autou)" and he related his vision (6:16, 11:35).
The metaphors of housing, clothing, and nakedness also appear in Greek and Hellenistic Jewish literature of the time. The Pythagoreans in particular referred to the body as a "tabernacle" or tent. Pseudo-Hippocrates (De Septimanis, 52.22) wrote that at death "the soul leaves the tabernacle of the body (apoleipousa hè psukhè to tou sòmatos skènos)" and similar statements can be found in Timaeus Locrus 104D and Pseudo-Plato, Axiochus 366A. Another appearance of the expression in Jewish literature can be found in 4 Baruch 6:6 (first century AD) which refers to one's "fleshly dwelling" (to sarkikò oikò) as a "tabernacle" (to skènòmati) and when one dies God will "take you out of your tent (arei se ek tou skènòmatos sou)". The thought in 2 Corinthians 5:1-2 is closest to that in Wisdom 9:15 (written by a Hellenistic Jew in the first century BC): "The perishable body weighs down the soul (phtharton sòma barunei psukhèn), and this earthy tent burdens the thoughtful mind (brithei to geòdes skènos noun poluphrontida)". Compare with Plato, Phaedo 81C where the physical body is said to be baru "heavy", embrithes "burdensome", and geòdes "earthly". Philo of Alexandria (De Somniis 1.122) uses oikos "dwelling, home" to refer to the body, saying that "the body is an abode bound up by nature with the soul (ton sumphua tès psukhès oikon to sòma)". As for Paul's use of gumnos "naked" as a metaphor for the disembodied state of the dead, this same metaphor occurs in Plato (cf. Cratylus 403, Gorgias 523). But Paul completely disagrees with Plato on the desirability of being gumnos in death; he sees it as a shameful and uncomfortable fate, arguing that God has better things in store for his followers. And Paul's description of the dead leaving their bodies to be with Christ has parallels in Philo of Alexandria as well. In one passage, Philo wrote that "it is not possible for one who is dwelling in the body (katoikounta en sòmati), in a race that is mortal, to be united with God (theò suggenesthai), but only he whom God delivers from that prisonhouse (ton hon ek tou desmòtèriou theos diarrhuetai)" (Legum Allegoriarum, 3.42), and in another he encouraged his readers to "rouse yourselves up and seek to accomplish a migration (metanastasin) from your own habitation (ton idion oikon) not to death but to immortality (ou thanaton all' athanasian)" (De Migratione Abrahami, 189).
Anyway, I know this is a lot of material to digest, but it gives some idea of the complexities and different perspectives floating around in Judaism and early Christianity.