Luke 1:35 says (paraphrased) that Holy Spirit would come upon Mary and the child born to her would be called God's Son.
This probably is a veiled reference to impregnation by an extraterrestrial similar to the angels before the Flood having intercourse with the daughters of men. Notice that men are always called 'sons of God' but women are always called 'daughters of men'.
Therefore, Jesus was, in all probability, an extraterrestrial. All these questions of perfect or imperfect are Paul's take on the sacrifice...really nothing to do with Jesus' actual physical existence - it just fits in with Paul's theology. Remember, Paul never met Jesus or had any dealings with him as a human being. The Gospels were all written long after Paul's letters and the Gospels were written to fit in with the PERFECT Son of God Paul had fashioned.
That's just an ALTERNATIVE explanation, but it does make some sense to me...ok, everybody, don't shoot the messenger!