Okay, McGrath, then you are different to the historicists like Ehrman and Casey, who do rely on the Gospels, and actually, the hypothetical sources underlying them. You seem to find the Historical Jesus in Paul. But all the passages from Paul that are used to demonstrate historicity are ambiguous at best, easily applying on the Celestial Jesus theory. For example, anything referring to Jesus' flesh, blood, and the simple fact that he died and resurrected. To address your example, these mentions of 'seed' are allegorical - Paul himself even indicates this (saying it outright with 'mother verses'). This should be obvious since he says Christians are of Abraham's seed, which obviously cannot be the case in a literal sense. Furthermore, Carrier opined that even the seed of David mention could be literal, but applying to a Celestial Jesus. As I show in this book, which I suppose you are yet to read, such ideas are quite common in ancient religion (Zoroastrianism, anyone?), and even in Jewish-Christian thought. Don't get me wrong, however, neither Carrier or I believe in the 'cosmic sperm bank'. From all the possibilities, we both prefer the allegorical reading.