Letter on the Council of Nicaea

⁷ And so too on examination there are grounds for saying that the Son is “one in essence” with the Father; not in the way of bodies, nor like mortal beings, for He is not such by division of essence, or by severance, no, nor by any affection, or alteration, or changing of the Father's essence and power (since from all such the unoriginate nature of the Father is alien), but because “one in essence with the Father” suggests that the Son of God bears no resemblance to the originated creatures, but that to His Father alone Who begot Him is He in every way assimilated, and that He is not of any other subsistence and essence, but from the Father. To which term also, thus interpreted, it appeared well to assent; since we were aware that even among the ancients, some learned and illustrious Bishops and writers have used the term “one in essence,” in their theological teaching concerning the Father and Son.