Texts Explained; Ninthly, John 10:30; 17:11, etc. Arianexplanation, that the Son is one with the Father in will and judgment; but so are all good men, nay things inanimate; contrast of the Son. Oneness between Them is in nature, because oneness in operation. Angels not objects of prayer, because they do not work together with God, but the Son; texts quoted. Seeing an Angel, is not seeing God. Ariansin fact hold two Gods, and tend to Gentile polytheism. Arianexplanation that the Father and Son are one as we are one with Christ, is put aside by the Regula Fidei, and shown invalid by the usage of Scripture in illustrations; the true force of the comparison; force of the terms used. Force of 'in us;' force of 'as;' confirmed by St. John. In what sense we are 'in God' and His 'sons.'
21 And for this reason also the words, 'that they may be one in Us,' have a right sense. If, for instance, it were possible for us to become as the Son in the Father, the words ought to run, 'that they may be one in You,' as the Son is in the Father; but, as it is, He has not said this; but by saying 'in Us' He has pointed out the distance and difference; that He indeed is alone in the Father alone, as Only Word and Wisdom; but we in the Son, and through Him in the Father. And thus speaking, He meant this only, 'By Our unity may they also be so one with each other, as We are one in nature and truth; for otherwise they could not be one, except by learning unity in Us.' And that 'in Us' has this signification, we may learn from Paul, who says, 'These things I have in a figure transferred to myself and to Apollos, that you may learn in us not to be puffed up above that is written.' The words 'in Us' then, are not 'in the Father,' as the Son is in Him; but imply an example and image, instead of saying, 'Let them learn of Us.' For as Paul to the Corinthians, so is the oneness of the Son and the Father a pattern and lesson to all, by which they may learn, looking to that natural unity of the Father and the Son, how they themselves ought to be one in spirit towards each other. Or if it needs to account for the phrase otherwise, the words 'in Us' may mean the same as saying, that in the power of the Father and the Son they may be one, speaking the same things; for without God this is impossible. And this mode of speech also we may find in the divine writings, as 'In God will we do great acts;' and 'In God I shall leap over the wall;' and 'In You will we tread down our enemies. ' Therefore it is plain, that in the Name of Father and Son we shall be able, becoming one, to hold firm the bond of charity. For, dwelling still on the same thought, the Lord says, 'And the glory which You gave Me, I have given to them, that they may be one as We are one.' Suitably has He here too said, not, 'that they may be in You as I am,' but 'as We are;' now he who says 'as', signifies not identity, but an image and example of the matter in hand.
22. The Word then has the real and true identity of nature with the Father; but to us it is given to imitate it, as has been said; for He immediately adds, 'I in them and You in Me; that they may be made perfect in one.' Here at length the Lord asks something greater and more perfect for us; for it is plain that the Word has come to be in us, for He has put on our body. 'And Thou Father in Me;' 'for I am Your Word, and since You are in Me, because I am Your Word, and I in them because of the body, and because of You the salvation of men is perfected in Me, therefore I ask that they also may become one, according to the body that is in Me and according to its perfection; that they too may become perfect, having oneness with It, and having become one in It; that, as if all were carried by Me, all may be one body and one spirit, and may grow up unto a perfect man. ' For we all, partaking of the Same, become one body, having the one Lord in ourselves. The passage then having this meaning, still more plainly is refuted the heterodoxy of Christ's enemies. I repeat it; if He had said simply and absolutely 'that they may be one in You,' or 'that they and I may be one in You,' God's enemies had had some plea, though a shameless one; but in fact He has not spoken simply, but, 'As Thou, Father, in Me, and I in You, that they may be all one.' Moreover, using the word 'as,' He signifies those who become distantly as He is in the Father; distantly not in place but in nature; for in place nothing is far from God, but in nature only all things are far from Him. And, as I said before, whoso uses the particle 'as' implies, not identity, nor equality, but a pattern of the matter in question, viewed in a certain respect.
23. Indeed we may learn also from the Saviour Himself, when He says, 'For as Jonah was three days and three nights in the whale's belly, so shall the Son of man be three days and three nights in the heart of the earth.' For Jonah was not as the Saviour, nor did Jonah go down to hades; nor was the whale hades; nor did Jonah, when swallowed up, bring up those who had before been swallowed by the whale, but he alone came forth, when the whale was bidden. Therefore there is no identity nor equality signified in the term 'as,' but one thing and another; and it shows a certain kind of parallel in the case of Jonah, on account of the three days. In like manner then we too, when the Lord says 'as,' neither become as the Son in the Father, nor as the Father is in the Son. For we become one as the Father and the Son in mind and agreement of spirit, and the Saviour will be as Jonah in the earth; but as the Saviour is not Jonah, nor, as he was swallowed up, so did the Saviour descend into hades, but it is but a parallel, in like manner, if we too become one, as the Son in the Father, we shall not be as the Son, nor equal to Him; for He and we are but parallel. For on this account is the word 'as' applied to us; since things differing from others in nature, become as they, when viewed in a certain relation. Wherefore the Son Himself, simply and without any condition is in the Father; for this attribute He has by nature; but for us, to whom it is not natural, there is needed an image and example, that He may say of us, 'As Thou in Me, and I in You.' 'And when they shall be so perfected,' He says, 'then the world knows that You have sent Me, for unless I had come and borne this their body, no one of them had been perfected, but one and all had remained corruptible. Work Thou then in them, O Father, and as You have given to Me to bear this, grant to them Your Spirit, that they too in It may become one, and may be perfected in Me. For their perfecting shows that Your Word has sojourned among them; and the world seeing them perfect and full of God, will believe altogether that You have sent Me, and I have sojourned here. For whence is this their perfecting, but that I, Your Word, having borne their body, and become man, have perfected the work, which You gave Me, O Father? And the work is perfected, because men, redeemed from sin, no longer remain dead; but being deified, have in each other, by looking at Me, the bond of charity. '
Source: Four Discourses Against the Arians (New Advent)