Most christian theologists point to a "Q" document that was likely the equivalent back then of "Jesus' greatest hits" of quotations.  Many find evidence to suggest that the Q document dates to the time that Jesus was preaching with key quotes his disciples could spread and remember.  Some gospels were clearly written decades later.  However, many dozens of gospels were summarily banned by the early catholic church.  Some point to critical gospels, even one by Mary Magdalene.  So one can ask why, in the new testament at the council of Nicaea, these many gospels were excluded and distilled down to the current new testament.

This, in fact is the basis for the DaVinci code.  The idea that the "sacred feminine" may have been deleted from the gospels and history.  I won't/can't argue that book, as it is not on topic.

In a much more general sense, the point is not whether the bible was written by man (it was), but whether there are lasting lessons, guidance and truth that can enhance our spirituality. 

Matthew