Many of Craig's arguments have been philosophized early on in human history, say by Aquinas who posits the Causal Argument for God's Existence, and by Anselm of Canterbury who uses a priori reasoning (arguing based on a set definition) to defend the same. Craig makes these approaches relevant today by supporting theism with logic, math and scientific findings. While Craig mentions some historical accounts about Jesus, it should be noted that this debate seeks to confirm God's existence/non-existence and in no way proves the need for religion nor the superiority of one religious sect vs another.
It is Flew's turn now, and he points out that he had prepared to explain/prove that there isn't enough proof of God's existence. He had not prepared to prove the opposite of Craig's stand, which is that God exists.