Christian argumentation – aimed at Christians, Jews, or pagans – was hardly static. Changes developed rapidly and broadly. The most important early innovator was Saul of Tarsus, become Paul, apostle to the gentiles. Identification of Paul's innovations is, as already noted, a matter of considerable dispute – internal Christian and modern scholarly. Since most modern researchers have concluded that Jesus' original message can no longer be reliably reconstructed, the precise nature of Paul's innovations can likewise not be recaptured. Moreover, the uncertainties and complexities associated with the purportedly Pauline epistles have obscured his message even more, giving rise to protracted and intense scholarly debate.

Perhaps the simplest starting point is our earlier observation that the main engagement portrayed in the Gospels involved Jesus and his Jewish contemporaries. As we move further into the evolution of the Jesus movement into Christianity, through the epistles of Paul (the earliest surviving stratum in the New Testament) and the narrative account in the Acts of the Apostles, the scene changes rather dramatically. While Paul continues to preach to his Jewish contemporaries, his fullest engagement is with gentiles, whom he attempts to attract to a seemingly new vision of Jesus, his mission, and his message.

The shift from intra-Jewish engagement to involvement with the gentile world brought a series of important changes in its wake. The most obvious change – reflected in Paul's own epistles and in the Acts of the Apostles – involves Jewish law.