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In Christianity, the doctrine of the Trinity states that God is one being who exists, simultaneously and eternally, as a mutual indwelling of three persons: the Father, the Son (incarnate as Jesus of Nazareth), and the Holy Spirit. Since the 4th century, in both Eastern and Western Christianity, this doctrine has been stated as "three persons in one God," all three of whom, as distinct and co-eternal persons, are of one indivisible Divine essence, a simple being. Supporting the doctrine of the Trinity is known as Trinitarianism. The majority of Christians are Trinitarian, and regard belief in the Trinity as a test of orthodoxy. Opposing, nontrinitarian positions that are held by some groups include Binitarianism (two deities/persons/aspects), Unitarianism (one deity/person/aspect), the Godhead (Latter Day Saints) (three separate beings) and Modalism (Oneness).
Neither the Old Testament nor New Testament uses the term "Trinity," though Trinitarians believe the concept is implicit in various biblical passages (see Scripture section below). The doctrine of the Trinity is the result of continuous exploration by the church of the biblical data, argued in debate and treatises. It was expressed in early writings from the beginning of the second century forward. The First Council of Nicaea in 325 AD established a nearly universal Trinitarian dogma and expressly rejected any heresies. The most widely recognized Biblical foundations for the doctrine's formulation are in the Gospel of John.citation needed]