Is Paul Part of the Birth of Christianity?

John Crossan in "The Birth of Christianity" does not consider Paul part of the birth of Christianity. He believes Paul is part of the growth and development of Christianity. Addtionally, he states that Paul is not as important theologically and historically in the first century as he is in the sixteenth century. "If you begin with Paul, you will interpret Jesus incorrectly; if you begin with Jesus, you will interpret Paul differently." (p. xxi)