[3] The term ὁμοούσιον, the accusative case form of ὁμοούσιος (homoousios, "consubstantial"),[2] was adopted at the First Council of Nicaea (325) in order to clarify the ontology of Christ.
[11][12][13][14][15][16][17][18][19][20][excessive citations] The early church theologians were probably made aware of this concept, and thus of the doctrine of emanation, taught by the Gnostics.
[22][23] The Valentinian Gnostic Ptolemy says in his letter to Flora that it is the nature of the good God to beget and bring forth only beings similar to, and consubstantial with, himself.
[32][33][34][35] Some theologians preferred the use of the term ὁμοιούσιος (homoioúsios or alternative uncontracted form ὁμοιοούσιος homoiooúsios; from ὅμοιος, hómoios, "similar", rather than ὁμός, homós, "same, common")[2] in order to emphasize distinctions among the three persons in the Godhead, but the term homoousion became a consistent mark of Nicene orthodoxy in both East and West.
According to this doctrine, Jesus Christ is the physical manifestation of Logos (or the Word), and consequently possesses all of the inherent, ineffable perfections which religion and philosophy attribute to the Supreme Being.
The several distinct branches of Arianism which sometimes conflicted with each other as well as with the pro-Nicene homoousian creed can be roughly broken down into the following classifications: All of these positions and the almost innumerable variations on them which developed in the 4th century were strongly and tenaciously opposed by Athanasius and other pro-Nicenes, who insisted on the doctrine of homoousion or consubstantiality, eventually prevailing in the struggle to define this as a dogma of the still-united Western and Eastern churches for the next two millennia when its use was confirmed by the First Council of Constantinople (381).
The Roman Emperor Theodosius had published an edict, prior to the Council of Constantinople, declaring that the Nicene Creed was the legitimate doctrine and that those opposed to it were heretics.
This notion, however, was also rejected at the Council of Nicaea, in favor of the Nicene Creed, which holds the Father and Son to be distinct yet also coequal, coeternal, and consubstantial divine persons.