A casual glance at the extensive Jewish polemic against the Trinity might lead one to think that Jewish theologians rejected any notion of a triune God per se. As our detailed study of the arguments has shown, the idea that God had a number of different or specific aspects was not repudiated by them out of hand. Some polemicists stated explicitly that the Trinity, in itself, was not an unacceptable doctrine. Yet the Christian Trinity was attacked with vehemence, and the Christian concept of a triune God was rejected as self-contradictory. The chief reason for this Jewish reaction lay in the Christian doctrine of incarnation, which was professed to be a concomitant of the belief in the Trinity. According to Christian teaching, one Person of the Trinity, the Son, assumed flesh in Jesus of Nazareth. While Jewish theologians might accept the notion that God has a number of aspects, they totally rejected the possibility that one such aspect did, or even could, become human. It was the doctrine of incarnation that most truly set apart the Jewish and Christian concepts of God.

Though there is no explicit statement in the New Testament claiming divinity for Jesus, and despite a number of verses which seem to disprove such a claim, the Church Fathers adopted the belief that he was both God and man. Those Christians who refused to accept this doctrine, such as the Ebionites or the Arians, who held that Jesus was only a man, were branded as heretics and excluded from the Church. The Nicene Creed, which effectively established the belief in the Trinity, also made the acceptance of Jesus as both God and man obligatory for the orthodox. Once this position was established, Christian thinkers found it necessary to explain how Jesus could be both God and man. This, in turn, led to controversies.