And when I speak of God you must be illumined at once by one flash of light and by three. Three in Individualities or Hypostases, if any prefer so to call them, or persons, for we will not quarrel about names so long as the syllables amount to the same meaning; but One in respect of the Substance—that is, the Godhead. For they are divided without division, if I may so say; and they are united in division. For the Godhead is one in three, and the three are one, in whom the Godhead is, or to speak more accurately, Who are the Godhead. Excesses and defects we will omit, neither making the Unity a confusion, nor the division a separation.
We would keep equally far from the confusion of Sabellius and from the division of Arius, which are evils diametrically opposed, yet equal in their wickedness. For what need is there heretically to fuse God together, or to cut Him up into inequality?
For to us there is but One God, the Father, of Whom are all things, and One Lord Jesus Christ, by Whom are all things; and One Holy Spirit, in Whom are all things; yet these words, of, by, in, whom, do not denote a difference of nature (for if this were the case, the three prepositions, or the order of the three names would never be altered), but they characterize the personalities of a nature which is one and unconfused. And this is proved by the fact that They are again collected into one, if you will read—not carelessly—this other passage of the same Apostle, “Of Him and through Him and to Him are all things; to Him be glory forever, Amen.”
The Father is Father, and is Unoriginate, for He is of no one; the Son is Son, and is not unoriginate, for He is of the Father. But if you take the word Origin in a temporal sense, He too is Unoriginate, for He is the Maker of Time, and is not subject to Time. The Holy Spirit is truly Spirit, coming forth from the Father indeed, but not after the manner of the Son, for it is not by Generation but by Procession (since I must coin a word for the sake of clearness); for neither did the Father cease to be Unbegotten because of His begetting something, nor the Son to be begotten because He is of the Unbegotten (how could that be?), nor is the Spirit changed into Father or Son because He proceeds, or because He is God—though the ungodly do not believe it. For Personality is unchangeable; else how could Personality remain, if it were changeable, and could be removed from one to another?