In traditional Christian theology, the doctrine of the Trinity is a mystery, which entails an admission that it is not entirely amenable to rational logic and understanding. Non-Christians, and many Christians who lack the appetite for metaphysical reasoning, may be forgiven for thinking that this allows for some equivocation, enabling Christianity to maintain contradictory positions without admitting it. Be that as it may, Christianity has never wavered in its claim to be a monotheistic religion. However the different persons of the Trinity are defined, they are to be understood as falling within the overarching unity of God. The notion that God is three as well as one, however, obviously entails a considerable qualification of monotheism.
Both Judaism and Christianity are committed to monotheism, the belief that ultimately there is only one God. Moreover, the break between Christianity and Judaism, particularly in their understanding of monotheistic doctrines, was not as sharp or complete as is sometimes assumed. The Synoptic Gospels can be reconciled quite easily with Jewish understandings of monotheism. The theology of Justin Martyr and Origen, in 2nd century C.E. Christianity, is not greatly removed from that of Philo, except that the Logos is now believed to be incarnate in the person of Jesus. This was, to be sure, a considerable difference, but the difference lay in the evaluation of a specific historical person rather than in the theological framework of monotheism or di-theism. Philo, for example, could speak of the patriarchs as empsychoi nomoi, or “the laws of God incarnate.” Only gradually did the Christian understanding of Christ and the Spirit evolve to the point where it was incompatible with any Jewish understanding of monotheism, and this process was only finalized in the 4th century C.E. Even the Nicene Creed (325 C.E.) begins with the confession, “I believe in one God [the Father].” Despite the logical anomalies of the Trinity, this confession is still repeated in Christian churches to this day.
From Aspects of Monotheism: How God is One, Meinhardt & Redford, 2003.
Both Judaism and Christianity are committed to monotheism, the belief that ultimately there is only one God. Moreover, the break between Christianity and Judaism, particularly in their understanding of monotheistic doctrines, was not as sharp or complete as is sometimes assumed. The Synoptic Gospels can be reconciled quite easily with Jewish understandings of monotheism. The theology of Justin Martyr and Origen, in 2nd century C.E. Christianity, is not greatly removed from that of Philo, except that the Logos is now believed to be incarnate in the person of Jesus. This was, to be sure, a considerable difference, but the difference lay in the evaluation of a specific historical person rather than in the theological framework of monotheism or di-theism. Philo, for example, could speak of the patriarchs as empsychoi nomoi, or “the laws of God incarnate.” Only gradually did the Christian understanding of Christ and the Spirit evolve to the point where it was incompatible with any Jewish understanding of monotheism, and this process was only finalized in the 4th century C.E. Even the Nicene Creed (325 C.E.) begins with the confession, “I believe in one God [the Father].” Despite the logical anomalies of the Trinity, this confession is still repeated in Christian churches to this day.
From Aspects of Monotheism: How God is One, Meinhardt & Redford, 2003.