The Trinity is a Christian doctrine, stating that God exists as three persons, or in the Greek hypostases, but is one being. The persons are understood to exist as God the Father, God the Son (incarnate as Jesus Christ), and God the Holy Spirit. Since the beginning of the third century the doctrine of the Trinity has been stated as "that the one God exists in three Persons and one substance, Father, Son, and Holy Spirit." Trinitarianism, belief in the Trinity, is a mark of Oriental and Eastern Orthodoxy, Roman Catholicism and all the mainstream traditions arising from the Protestant Reformation, such as Anglicanism, Lutheranism and Presbyterianism; and the Oxford Dictionary of the Christian Church describes the Trinity as "the central dogma of Christian theology".The Oxford Dictionary of the Christian Church (Oxford University Press, 2005 ISBN 978-0-19-280290-3), article Trinity, doctrine of the

This doctrine is in contrast to Nontrinitarian positions which include Binitarianism (one deity/two persons), Unitarianism (one deity/one person), the Oneness belief held by certain Pentecostal groups, Modalism, and The Church of Jesus Christ of Latter-day Saints' view of the Godhead as three separate beings who are one in purpose rather than essence.

The doctrine of the Trinity was of particular importance historically. The conflict with Arianism and other competing theological concepts during the fourth century became the first major doctrinal confrontation in Church history. It had a particularly lasting effect within the Western Roman Empire where the Germanic Arians and the Nicene Christians formed segregated social orders.

Etymology

The corresponding word in Greek is "lang: Τριάς", meaning "a set of three" or "the number three."

The first recorded use of this Greek word in Christian theology (though not about the Divine Trinity) was by Theophilus of Antioch in about 170. He wrote: W.Fulton in the "Encyclopedia of Religion and Ethics"

"In like manner also the three days which were before the luminaries, are types of the Trinity Τριάδος, of God, and His Word, and His wisdom. And the fourth is the type of man, who needs light, that so there may be God, the Word, wisdom, man."

Tertullian, a Latin theologian who wrote in the early third century, is credited with using the words "Trinity," "person" and "substance" to explain that the Father, Son and Holy Spirit are "one in essence – not one in Person."

About a century later, in 325, the First Council of Nicaea established the doctrine of the Trinity as orthodoxy and adopted the Nicene Creed that described Christ as "God of God, Light of Light, very God of very God, begotten, not made, being of one substance (homoousios) with the Father."