The interpolation of Greek thought into Christian doctrine was supposed to have happened well after the second century A.D. But the first century Christians clearly believed that people had spirits. Peter wrote:
For Christ also hath once suffered for sins, the just for the unjust, that he might bring us to God, being put to death in the flesh, but quickened by the Spirit: by which also he went and preached unto the spirits in prison; which sometime were disobedient, when once the longsuffering of God waited in the days of Noah, while the ark was a preparing, wherein few, that is, eight souls were saved by water. (1 Peter 3:18-21)Who were these spirits in prison? A few verses later, he writes:
For the time past of our life may suffice us to have wrought the will of the Gentiles, when we walked in lasciviousness, lusts, excess of wine, revellings, banquetings, and abominable idolatries: wherein they think it strange that ye run not with them to the same excess of riot, speaking evil of you who shall give account to him that is ready to judge the quick and the dead. For for this cause was the gospel preached also to them that are dead, that they might be judged according to men in the flesh, but live according to God in the spirit. (1 Peter 4:4-6)Here Peter talks about the wickedness and lasciviousness of the gentiles, but points out that they, as Christians, are expected to live a higher law in that they know that they'll one day stand before Christ, the judge of the living and the dead. And because of this, the gospel was preached to the spirits of the dead, that they might be judged like those in the flesh (the living), yet exist as those in the spirit (the dead).
In the third century A.D., the great Christian scholar Origen, trying to recall what the apostles taught concerning life after death, said:
After death, I think the saints go to Paradise, a place of teaching, a school of the spirits in which everything they saw on earth will be made clear to them. Those who were pure in heart will progress more rapidly, reaching the kingdom of heaven by definite steps or degrees."Interestingly, Origen believed that 1) much of the knowledge that was lost by the first century Christians would remain lost until the times of the "restoration of all things;" 2) that all humans have a pre-mortal existence (a belief that was subsequently condemned by the church as a heresy); and 3) that there are "three celestial levels like the sun, the moon and the stars." (See 1 Corinthians 15). The Greeks believed in reicarnation -- a doctrine conspicuously missing from the Christian church.
Not only does the pseudopigrapghical Apocalypse of Abraham teach that man has a spirit, so does the apocryphal Book of Enoch and the book of 2 Maccabees. The significance of all this is that we have pre-Christian Jewish references, orthodox Christian references, apocryphal Christian references and numerous statements by early church fathers, all teaching that there is a spirit in man. Not one of these teach reincarnation or contained a single reference to Ecclesiastes 9:5 (a book which in my view shouldn't even be in the Bible; neither should the Song of Solomon). My point is that we have so many writings available that if the first century saints had believed in the soul sleeping doctrine, we'd know about it!