Originally Posted by Wangdoodle
From Catholic Encyclopedia, Newadvent.org
The doctrine of the Trinity is formally taught in every class of ecclesiastical writing. From among the apologists we may note Justin, "Apol." I, vi; Athenagoras, "Legat: pro Christ.", n. 12. The latter tells us that Christians "are conducted to the future life by this one thing alone, that they know God and His Logos, what is the oneness of the Son with the Father, what the communion of the Father with the Son, what is the Spirit, what is the unity of these three, the Spirit, the Son, and the Father, and their distinction in unity." It would be impossible to be more explicit. And we may be sure that an apologist, writing for pagans, would weigh well the words in which he dealt with this doctrine.
Amongst polemical writers we may refer to Irenaeus, "Adv. haer.", I, xxii, IV, xx, 1-6. In these passages he rejects the Gnostic figment that the world was created by aeons who had emanated from God, but were not consubstantial with Him, and teaches the consubstantiality of the Word and the Spirit by Whom God created all things.
Yet further evidence regarding the Church's doctrine is furnished by a comparison of her teaching with that of heretical sects.
The controversy with the Sabellians in the third century proves conclusively that she would tolerate no deviation from Trinitarian doctrine. Noetus of Smyrna, the originator of the error, was condemned by a local synod, about A.D. 200. Sabellius, who propagated the same heresy at Rome c. A.D. 220, was excommunicated by St. Callistus.
In Scripture there is as yet no single term by which the Three Divine Persons are denoted together. The word trias (of which the Latin trinitas is a translation) is first found in Theophilus of Antioch about A.D. 180. He speaks of "the Trinity of God [the Father], His Word and His Wisdom ("Ad. Autol.", II, 15). The term may, of course, have been in use before his time. Afterwards it appears in its Latin form of trinitas in Tertullian ("De pud." c. xxi). In the next century the word is in general use. It is found in many passages of Origen ("In Ps. xvii", 15). The first creed in which it appears is that of Origen's pupil, Gregory Thaumaturgus. In his Ekthesis tes pisteos composed between 260 and 270, he writes:
There is therefore nothing created, nothing subject to another in the Trinity: nor is there anything that has been added as though it once had not existed, but had entered afterwards: therefore the Father has never been without the Son, nor the Son without the Spirit: and this same Trinity is immutable and unalterable forever (P. G., X, 986).
