Taking a secular view, it's an interesting book, for sure.
...It is hard for us today to imagine the Jesus story being consciously created, but this is because we have misunderstood ancient spirituality. Myths were not seen as untruths as they are now. They were understood as allegories of spiritual initiation, which encoded profound mystical teachings. Reworking old myths to create new ones was a standard practice in the ancient world...
...Whilst our ideas clearly rewrite history, we do not see ourselves as undermining Christianity. On the contrary we are suggesting that Christianity is in fact richer than we previously imagined. According to the original Gnostic Christians, the Jesus story is a perennial myth with the power to impart the mystical experience of Gnosis, which can transform each one of us into a Christ, not merely a history of events that happened to someone else two thousand years ago.
http://www.vexen.co.uk/books/jesusmysteries.html
The thing about "initiations" is that you've gotta believe them for them to have any effect