Rather than saying that the pre-rabbinical concept of life after death was vague, it might be more accurate to say that there were an assortment of varied concepts thoughout early Judaism that reflected different influences, a portion of which were far from vague but relished in the amount of detail related about the (future) condition of the dead (which is especially the case in apocalyptic literature). Judea had influences from both the East and the West; from the former came the notion of the resurrection of the body from the Persians and from the West came Hellenistic ideas on the incorporeality of the soul and its journeys after death. If having an intermediate state in heaven between death and resurrection seems awkward, it is probably because it mixes together ideas that originated in different milieus. Platonic, Stoic, and Pythagorean anthropology regarded the soul liberated from the body at death as entering a blessed state in an ethereal realm, whether the Isles of the Blessed (as in Plato), the Milky Way (as in Pythagoras), or among the stars in general. Some Jews had a concept of the soul's immortality without any implication of a future resurrection (as in Wisdom 2:22, 3:1-4, 4 Maccabees 9:8, 13:17, 14:5-6, 17:17-19, 18:23, Philo of Alexandria, De Opificio Mundi 134-135, De Abrahamo 258, etc.), whereas others had a strictly physical, corporeal notion of resurrection (cf. 1 Enoch 25:4-6, 2 Maccabees 7:9-14, 23, 29, 14:46, 4Q385 2:5-9), and then others had a compromise in which those in the resurrection were no longer fleshly but spiritual with the characteristics of heavenly bodies (cf. Daniel 12:2-3, 1 Enoch 58:2-3, 62:15-16, 91:10, 92:3-5, 104:2-7, Matthew 22:30, Luke 20:27-26, 1 Corinthians 15:35-55, Philippians 3:10-11, 20-21, 2 Baruch 51:3-12).
Heaven as the abode of the soul in the intermediate state between death and resurrection is clearly conceived as such in Josephus:
Josephus, Bellum Judaicum 3.374-376: "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".
Revelation has a similar concept. The "souls" (psukhas) of "all the people who had been killed on account of the word of God" currently reside in heaven "underneath the altar" and they "were told to be patient a little longer until the roll [of the matyred dead] was complete and their fellow servants and brothers had been killed just as they had been" (6:9-11); 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. It is then at this point that "those who refused to worship the beast or his statue and would not have the brand-mark on their forehead and hands came to life" in the "first resurrection" (20:4-5). The souls of the dead therefore wait in heaven in between the time of their martyrdom and their resurrection.
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). Maybe the Pauline omission of a future destiny on earth is a simplication that removes the complication of movement back and forth of the dead between earth and heaven. The scenario in Revelation however is even more complex, as it has the heavenly abode itself coming to a recreated earth (ch. 21-22).
The summary of the beliefs of the Essenes, Pharisees, and Sadducees by Hippolytus gives a fairly useable comparison. As for the Essenes, "the idea of the resurrection (anastaseós) has strength among them for they acknowledge both that the flesh will rise again (tén sarka anastésesthai), and that it will be immortal, in the same manner as the soul is already immortal (édé athanatos estin hé psukhé). And they maintain that the soul, when seperated in the present life, departs into one place, which is well ventilated and full of light where, they say, it rests until judgment" (Adversus Haereses 9.26-27). As for the Pharisees, "these likewise acknowledge that there is a resurrection of flesh (sarkos anastasin), and that the soul is immortal (psukhén athanaton), and that there will be a judgment and conflagration, and that the righteous will be imperishable (aphthartous), but that the wicked will be punished forever in unquenchable fire (eisaei kolasthésesthai en puri asebestó)" (9.28). But in the case of the Sadducees, "they deny that there is a resurrection, not only of flesh (anastasin ou monon sarkos) but they also suppose that the soul does not endure (psukhén mé diamenein). It is only the life (monon to zén), and it is on account of this that man has been created. However, the idea of the resurrection is fulfilled in this: in dying and leaving behind children upon the earth. But after death one expects to suffer nothing, either bad or good. For there will be a dissolution both of soul and body (lusin kai psukhés kai sómatos), and man passes into non-existence (eis to mé einai khórein), similarly also with the material of the animal kingdom" (9.29).
Similar statements about the Sadducees occur in Josephus (Bellum Judaicum 2.165, Antiquitates 18.16), that they do away with "the survival of the soul (phukhés tén diamonén) and punishments down in Hades and rewards" and teach that "souls perish together with bodies" (tas phukhas sunaphanizei tois sómasi). 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 perspective, possibly influenced by Greek Epicureanism, is best represented in the OT in the books of Ecclesiastes and Sirach, which both have no concept of a future resurrection and, in the case of Ecclesiastes, argues against it: "The living know that they will die but the dead know nothing; they have no further reward, and even the memory of them is forgotten. Their love, their hate, and their jealousy have long since vanished. Never again will they have a part in anything that happens under the sun" (9:5-6). This is of course a favorite proof-text of the Society in its own eschatology but it stands in tension with NT references to resurrection, which claim that indeed there is a "further reward" and that the resurrected will again have life and "have a part in what happens under the sun". The Sadducee annihilationst view (that man "passes into nonexistence" at death) is essentially grafted onto the Pharisee/Essene concept of resurrection from the NT, resulting in a conceptually difficult JW doctrine that nothing of the original person survives death and yet somehow the same person is brought back to life. I do not think such a combination is ever attested in early Jewish and Christian references to life after death, for all the variety and complexity of pre-rabbinical beliefs about death and the afterlife.
