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What does homoousios mean in the Nicene Creed?
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Christology
The Transfiguration, the nature of Jesus as the Son of God being revealed to the apostles Peter, James, and John, mosaic icon, early 13th century; in the Louvre, Paris.
In the context of Christology, the term homoousios is a Greek word meaning "of one substance." It was incorporated into the Nicene Creed to formally affirm that God the Son and God the Father share the same divine essence.12
The term was adopted during the First Council of Nicaea in 325 CE to resolve a major theological controversy regarding the nature of Christ. Specifically, it was used to condemn Arianism, a doctrine that argued Christ was a created being rather than fully divine. By declaring that Christ is homoousios with the Father, the council established the definitive orthodox belief in the full divinity of the Son within the Trinity. This terminology was later reaffirmed at the First Council of Constantinople in 381 CE.12