Homoousion in the context of "Trinitarianism"

God the Son (Greek: Θεὸς ὁ Υἱός, Latin: Deus Filius) or God the Word (Greek: Θεὸς ὁ Λόγος, Latin: Deus Verbum) is the second Person of the Trinity in Christian theology. According to mainstream Christian doctrine, God the Son, in the form of Jesus Christ, is the incarnation of the eternal, pre-existent divine Logos (Koine Greek for "word") through whom all things were created. Although the precise term "God the Son" does not appear in the Bible, it serves as a theological designation expressing the understanding of Jesus as a part of the Trinity, distinct yet united in essence with God the Father and God the Holy Spirit (the first and third Persons of the Trinity respectively).

In Christianity, God is the eternal, supreme being who created and preserves all things. Christians believe in a monotheistic conception of God, which is both transcendent (wholly independent of, and removed from, the material universe) and immanent (involved in the material universe). Christians believe in a singular God that exists in a Trinity, which consists of three Persons: God the Father, God the Son, and God the Holy Spirit. Christian teachings on the transcendence, immanence, and involvement of God in the world and his love for humanity exclude the belief that God is of the same substance as the created universe (rejection of pantheism) but accept that God the Son assumed hypostatically united human nature, thus becoming man in a unique event known as "the Incarnation".

Early Christian views of God were expressed in the Pauline epistles and the early Christian creeds, which proclaimed one God and the divinity of Jesus. Although some early sects of Christianity, such as the Jewish-Christian Ebionites, protested against the deification of Jesus, the concept of Jesus being one with God was accepted by the majority of Gentile Christians. This formed one aspect of the split of early Christianity and Judaism, as Gentile Christian views of God began to diverge from the traditional Jewish teachings of the time.

Arius (/əˈraɪəs, ˈɛəri-/; Koine Greek: Ἄρειος, romanized: Áreios; 250 or 256 – 336) was a Cyrenaic presbyter and ascetic. He has been regarded as the founder of Arianism, which holds that Jesus Christ was not coeternal with God the Father, but was rather created by God the Father. Arian theology and its doctrine regarding the nature of the Godhead showed a belief in radical subordinationism, a view notably disputed by 4th century figures such as Athanasius of Alexandria.

Constantine the Great's formal decriminalization of Christianity into the Roman Empire entailed the convention of ecumenical councils to remove theological divisions between opposing sects within the Church. Arius's theology was a prominent topic at the First Council of Nicaea, where Arianism was condemned in favor of Homoousian conceptions of God and Jesus. Opposition to Arianism remains embodied in the Nicene Creed, described as "a deliberately anti-Arian document." Nevertheless, despite concerted opposition, Arian churches persisted for centuries throughout Europe (especially in various Germanic kingdoms), the Middle East, and North Africa. They were suppressed by military conquest or by voluntary royal conversion between the fifth and seventh centuries.

The Athanasian Creed—also called the Quicunque Vult (or Quicumque Vult), which is both its Latin name and its opening words, meaning "Whosoever wishes"—is a Christian statement of belief focused on Trinitarian doctrine and Christology. Used by Christian churches since the early sixth century, it was the first creed to explicitly state the equality of the three hypostases of the Trinity. It differs from the Nicene-Constantinopolitan Creed and the Apostles' Creed in that it includes anathemas condemning those who disagree with its statements, as does the original Nicene Creed.

Widely accepted in Western Christianity, including by the Roman Catholic Church, Lutheran Churches (it is part of the Lutheran confessions set out in the Book of Concord), Anglican Churches, Reformed Churches, and ancient liturgical churches, the Athanasian Creed has been used in public worship less frequently, with exception of Trinity Sunday. However, part of it can be found as an "Authorized Affirmation of Faith" in the main volume of the Common Worship liturgy of the Church of England published in 2000. Despite falling out of liturgical use, the creed's influence on current Protestant understanding of trinitarian doctrine is clear.

Hosius of Corduba (c. 256–359), also known as Hosius the Confessor, Osius or Ossius, was a bishop of Corduba (now Córdoba, Spain) and an important and prominent advocate for Homoousion Christianity during the period when the Arian controversy divided early Christianity.

He probably presided at the First Council of Nicaea and also presided at the Council of Serdica.