[user104658]

It seems simple enough to me; God created a physical human body (which you could call "his son", physically, a human body that he created) but then he put himself, or a humanised incarnation of himself, into that physical body. The body is just a vehicle (an avatar) for the "soul" of God himself, which existed before, and continued to exist after, the body. The body itself didn't have its own separate individual self, however, the "human life" and experiences that God lived inside that body could be considered distinct from the rest of his existence. You could argue that the experience of being human himself altered his understanding of humanity, hence the tonal differences between the new and old testaments, and the general insistence that anything contradictory to the old testament contained in the new testament should be considered to "override" the old testament.

I kind of wish there was truth in it, it's a fascinating story really. I get why people get so invested in it.