As we have seen, God’s people of old steadfastly held to the absolute singularity of God. For them, when speaking of God, one equaled one, and that one was their Father. However, post-biblical Christian theology saw a departure from that uncompromising monotheism. Binitarian and Trinitarian theologies proposed a different understanding of God. Binitarianism is the belief that two distinct persons are the one God. Trinitarianism is the belief that three persons are one God. In the new monotheism, the simplicity of the prophets was displaced by a complex view of Deity in which one God is two or three persons. Here, God’s own spirit is often worshiped as a separate person of Deity, and the LORD’s Messiah is honored not only as his greatest anointed king — but also as being God himself. Developed after the Bible was written, multi-person theologies proposed that two or three are the same Deity in terms of substance, yet different persons within that substance. Confusing to even think about, the terms of such formulas are found in post-biblical literature and church creeds but not in the Bible itself. Clearly, this new definition of monotheism would be inconceivable to the LORD’s prophets and his people of old. He told them that “he is God and there is no one else; he is God and there is no one like him” (Isa. 46:9). They believed him! Their faith began and ended on the point that their Father alone is God.
Over the centuries a poly-personal God has not held attraction for Orthodox Judaism. For the great majority of Jews, multi-person monotheism is an oxymoron. They have viewed it as syncretistic and a fatal compromise regarding the absolute sovereignty of the one who alone is God. Whether Hindu, post-biblical Christian, or other, all concepts of a multi-person monotheism have been rejected by faithful Jews.
Judaism remains a devoted guardian of original monotheism. Theirs is a pure, uncomplicated view of the singularity of God. Scholars of various backgrounds sometimes refer to the “strict” monotheism of the Jews. But what then is “un-strict” monotheism? Can it rightly be called monotheism at all? The Jewish objection is clear: Does not multi-person monotheism — at its core — represent a departure from the Hebrew Bible? Does it not introduce others to be worshiped as God through a sort of theological back door? Is it not an attack on the sole sovereignty of the Father?
Christ and the earliest Christians were entirely devoted to absolute monotheism. Jesus and the apostles were all dedicated Jews. The New Testament was written by people who were strict monotheists. They all knew the Scriptures in which the Father had declared himself to be the only one who is God. Multi-person monotheism as a Christian concept developed in post-biblical times. In the second through the fifth centuries CE, Gentile Christians misinterpreted and re-interpreted the Bible in terms of multiple persons as one God. Today, many Trinitarian scholars acknowledge that the Trinity is a post-biblical concept. For example, Baptist scholar Roger Olson and Episcopalian theologian Christopher Hall candidly write:
The doctrine of the Trinity developed gradually after the completion of the New Testament in the heat of controversy… The full blown doctrine of the Trinity was spelled out in the fourth century at two great ecumenical (universal) councils: Nicaea (325 A.D.) and Constantinople (381 A.D.) … Both the practices and documents of the church finally led early Christian leaders to propose a trinitarian model of God, but the formation of this model took place over many years and in many contexts., 
Trinitarian scholar William C. Placher in his History of Christian Theology admits that the Cappadocians, who were central to the development of Trinitarian theory in the 4th century CE, “were deeply influenced by Platonic [Greek] philosophy” and that “modern theologians often have a tough time restating their theory of the Trinity in plausible form apart from those Platonic assumptions.”
There are those who place absolute confidence in post-biblical church councils and Christian tradition. For them, it is not disconcerting that the doctrine of the Trinity was developed by theologians in the centuries after the Bible was written. However, it should be alarming for those who see the Bible as the inspired and best source for all matters of faith to find leading Trinitarian scholars speaking of this doctrine as “developing gradually after the completion of the New Testament” under the sway of men who were “deeply influenced by Platonic philosophy.”
Gill, J. Dan (2016). The Trinity – A Christian Dilemma. In, The One: In Defense of God (pp. 92-94). Nashville, TN: 21st Century Reformation Publishing.
 Oneness theology is a third view and represents a variation on the same theme. In Oneness, rather than persons, God is pictured as having multiple manifestations. It is often difficult to see, however, any real difference between multiple persons and the supposed manifestations.
 Some Trinitarian scholars do not like the term persons on the ground that it does not adequately reflect the Greek word which was used in the post-biblical formation of the doctrine of the Trinity (one ousia in three hypostaseis). However, scholars do not propose any clear alternative and the use of “persons” is customary among Christians. At the root of the problem is that neither the word hypostaseis nor any other Hebrew or Greek term that would rightly be translated “persons” is used in the Bible to refer to God. There simply is no use of the words “three persons (hypostaseis) in one essence (ousia)” in the New Testament. God is a single “self ” — one individual — not two or three persons. There is in fact no place in the Bible where the word “three” is used to refer to the true God.
 The people of the Bible never thought of God’s spirit and his Messiah as being persons of co-Deity with the Father. The spirit of God was not understood to be a separate person from the Father, and the Messiah was seen as being his only begotten human son.
 Without scriptural definitions for the new terms they employed, there were severe post-Nicaea debates regarding critical meanings. Notably, the meaning of the word “substance” in this context was wrestled over. The struggle centered on the subtle differences in the Greek terms homoousios and homoiousios. (Hence the adage, “an iota’s worth of difference.”) Other crucial terms also presented challenges, including hypostasis (Greek) versus substantia (Latin). Of course, the essential problem with all of this was that these post-biblical Gentile Christians were debating issues which were entirely foreign to both the Hebrew Bible and the New Testament. God’s people in the Bible believed that God “just is” one.
 While Judaism at large has rejected any form of multi-person monotheism, there is a contingent of Jews who believe in Jesus as the Christ (Messianic Jews). While wonderfully devout people, in embracing Jesus as Messiah they have also often crossed over from absolute monotheism to post-biblical multi-person monotheism. That is a tragedy to the entire Jewish community. With Trinitarianism as a barrier, Jews at large are unmoved by the witness of the Messianic contingency. Post-biblical theology proposing that Jesus is God has likely hindered many Jews from embracing him as God’s Messiah. The author of this book has met some Messianic Jews who are Christian Monotarian. They have embraced Jesus as the Messiah while worshiping his Father as the only true God ( John 17:3).
 There are many writings which chronicle the development of multi-person monotheism in post-biblical Christianity. For a short overview of the Nicene Council (325 CE) see Peter Partner, Christianity —The First Two Thousand Years (London: Seven Oaks, 2002), 59 ff. For an enlightening history and review of issues surrounding that council also see Richard E. Rubenstein, When Jesus Became God (San Diego, CA: Harcourt, Inc., 2000).
 Olson and Hall indicate that “Patristic trinitarian theology is grounded in a number of significant foundations.” There they include the Scriptures but also “early liturgies,” “short creedal statements,” “worship practices” and “the overarching rule of faith of the early church.” Roger E. Olson and Christopher A. Hall, The Trinity (Grand Rapids: Wm. B. Eerdmans Publishing Co., 2002), 2, 15.
 Dr. Dale Tuggy believes that Olson and Hall’s assessment that “the full blown doctrine of the Trinity was spelled out” in the two fourth-century councils is to say too much. Tuggy indicates that “If we scour the documents of the First Council of Constantinople (381 CE), we will not see them using ‘God’ to refer to all three together.” Tuggy does see the latter council as being “about the time” that the switch occurred. Dale Tuggy, personal correspondence, December 5, 2014. Also see, http://trinities.org/blog/10-steps-towards-gettingless- confused-about-the-trinity-8-trinity-vs-trinity/.
 William C. Placher, A History of Christian Theology (Philadelphia: The Westminster Press, 1983), 78.