De trinitate

Of the same Athanasius: Believe in one nature of Father and Son and Holy Spirit, the divinity, and in three hypostases, Father, Son, and Holy Spirit, just as we have been baptized. For he says, "Go forth, teach all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit." One nature, because to glorify more than one and to cut the one divinity into many gods is the way of the Greeks; three hypostases, that is, persons, so that the opinion of the Jews may have no place, and so that the Father may not be barren and without reason, from whom all fatherhood comes; and so that the Word may not be inferior to our word, lacking Spirit; and so that perfection may be in three perfect hypostases. For the image in us of mind, word, and spirit is Father, Son, and Spirit. When you hear "Spirit," understand a holy hypostatic Spirit. We are perishable, and our spirit is dissolved; but the Spirit of the immortal is certainly immortal, as a hypostatic substance. Therefore, there is one nature of the three hypostases, the divinity, and one will, and one energy, one power, one purpose and movement, and one radiance of the splendor of the three. God the Father, God the Son, God the Spirit, the three are one; God the Father is perfect, the Son is perfect, the Holy Spirit is perfect; of the same honor, of the same authority.

Creator of all beings, and sustaining, and providential, similarly all things to the three, and unalterably and identically, as many as pertain to being, and as many as pertain to not being something, and as many as pertain to how it relates to created things, and as many as pertain to activity, and as many as pertain to power, as many as pertain to eternity, and as many as are said to be by preeminence or by causality. For example, being the same, being incorporeal, being incomprehensible, ruling, creating, deifying, being able, being eternal, being a beginning beyond beginning, being an essence beyond essence, being called light. But darkness is what is said symbolically, such as being angry and wrathful, sleeping and being awake. All these things we attribute to the one nature, not from what is according to it do we manifest or conceive it, but from what is around it. Knowing then the one nature of the three hypostases, differing in nothing else but these properties—I mean begetting and being begotten and proceeding, and that one is Father, another Son, another Spirit; and that the Father is begetter and producer, begetter of the Son, producer of the Spirit; the Son is offspring, the Spirit is product. And the Father is unbegotten, the Son is begotten with two n's, the Spirit is emanated. And the Father is cause, the Son and the Spirit are caused. And the Father is producer, the Son is only Son, and the Spirit is that which proceeds.

For they do not depart from their proper characteristics: neither the Father from being Father, nor the Son from being Son, nor the Spirit from being Spirit; but the substance is common, the divinity of the three is one, as it were three lights united with one another and not confused. These things are sufficient to know concerning theology. The end, and thanks be to God.