The Catholic Church developed a doctrine of God which had never been held by Jews or Christians before.
"The doctrine of one God, the Father and creator, formed the background and indisputable premiss of the Church's faith. Inherited from Judaism, it was her bulwark against pagan polytheism. . . . The problem for theology was to integrate with it, intellectually, the fresth data of the specifically Christian revolution. . . . No steps had been taken so far, however, to work all these complex elements into a coherent whole. The Church had to wait for more than three hundred years for a final synthesis, for not until the council of Constantinople (381) was the formula of one God existing in three co-equal Persons formally ratified." J.N.D. Kelly, Early Christian Doctrines, second ed., Harper & Row, pp. 87, 88.
"The idea of the trinity has precedents in the Bible, even though a fullfledged doctrine of the trinity is not to be found there. Christian thinkers formulated the doctrine of the trinity largely during the fourth and fifth centuries after Christ." Richard Rice, The Reign of God.
"Trinity (theology), in Christian theology, doctrine that God exists as three persons - Father, Son, and Holy Spirit - who are united in one substance or being. The doctrine is not taught explicitly in the New Testament, where the word God almost invariably refers to the Father; but already Jesus Christ, the Son, is seen as standing in a unique relation to the Father, while the Holy Spirit is also emerging as a distinct divine person. The term trinitas was first used in the 2nd century, by the Latin theologian Tertullian, but the concept was developed in the course of the debates on the nature of Christ (see Christology). In the 4th century, the doctrine was finally formulated; using terminology still employed by Christian theologians, the doctrine taught the coequality of the persons of the Godhead." "Trinity (theology)," Microsoft® Encarta® Encyclopedia 99. © 1993-1998 Microsoft Corporation. All rights reserved.
"Q. Do you observe other necessary truths as taught by the Church, not clearly laid down in Scripture?
"A. The doctrine of the Trinity, a doctrine the knowledge of which is certainly necessary to salvation, is not explicitly laid down in Scripture, in the Protestant sense of private interpretation." A Doctrinal Catechism, Stephen Keenan, p. 351.
"Our opponents sometimes claim that no belief should be held dogmatically which is not explicitly stated in Scripture. . . . But the Protestant Churches have themselves accepted such dogmas as the Trinity for which there is no such precise authority in the Gospels." Life Magazine, October 30, 1950.