Summary of Chapter 5
The 5th 'lie' that Young brings up is that 'God is a Christian'. He's making a point here about religion in general. In his view, Jesus challenges every religious category. Christianity is not so much a religion as the end of all religions. Humans tend to categorize people according to religion, but God (according to Young) sees all people as 'beloved insiders'. What is important is following Christ, not a religious label.
I essentially agree with Young's point that Jesus brought the end of (the need for) religion (in the sense of human's searching for God and attempting to earn his favor with sacrifices). Any suggestion that God only cares for people who fit under the label of 'Christian' is ruled out by God's character. But does God really relate to everyone as a 'beloved insider'? I think it would be more accurate to say that God loves everyone and invites them into the trinitarian dance than to say everyone already is an insider. Young's meaning seems unclear. He clearly says that all people need to discover Jesus, but he simultaneously seems to be suggesting that even people who haven't yet discovered Jesus are already insiders in some sense (inside the scope of God's love, perhaps).