By Water & Blood

Chapter 19: That just as the Father and the Son are said to be one, so also will all the saints be

And indeed in this way we shall all become one with the Father and the Son. For just as he said that he and the Father were one, saying, “I and my Father are one,” so too he prays that all of us, in imitation of him, may share in the same unity—not, as Marcellus has it, by the Word being united to God and conjoined with him in essence, but as the Truth bore witness, the Saviour himself saying, “The glory which thou gavest me I have given them; that they may be one, even as we are one: I in them, and thou in me, that they may be made perfect in one.” For so, then, the apostolic oracle too will reach its fulfilment, which said, “that God may be all in all.”

And since Marcellus and those who Sabellianize in the same manner as he are accustomed to use three sayings in trying to show that the Father and the Son are one—at one time harping on “I and my Father are one,” at another on “The Father is in me, and I in the Father,” and on “He that hath seen me hath seen the Father”—then against “I and my Father are one” we must bring forward to them the passage before us, in which he prays for his disciples that they all may obtain the same union. He says, then, “that they may be one, even as we are one:

I in them, and thou in me, that they may be made perfect in one.” And against “The Father is in me, and I in the Father” we shall set his voice again, in which, praying for them, he said, “As thou, Father, art in me, and I in thee, that they also may be in us; and the glory which thou gavest me I have given them.” By this he clearly establishes that the Father is in him in the same way in which he wishes him to be in us—not that he and the Father are one according to one hypostasis, but that, as the Father has imparted to him his own glory, so he too likewise, imitating the Father, imparts it to his own.

Therefore he says, “And the glory which thou gavest me I have given them; that they may be one, even as we are one,” and “As thou, Father, art in me, and I in thee, that they also may be in us.” So, then, the Father and the Son are one according to the communion of glory; and imparting this to his disciples, he deemed them worthy of the same union.