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.'
16 For if it be not so, but the Word is a creature and a work out of nothing, either He is not True God because He is Himself one of the creatures, or if they name Him God from regard for the Scriptures, they must of necessity say that there are two Gods, one Creator, the other creature, and must serve two Lords, one Unoriginate, and the other originate and a creature; and must have two faiths, one in the True God, and the other in one who is made and fashioned by themselves and called God. And it follows of necessity in so great blindness, that, when they worship the Unoriginate, they renounce the originate, and when they come to the creature, they turn from the Creator. For they cannot see the One in the Other, because their natures and operations are foreign and distinct. And with such sentiments, they will certainly be going on to more gods, for this will be the essay of those who revolt from the One God. Wherefore then, when the Arians have these speculations and views, do they not rank themselves with the Gentiles? For they too, as these, worship the creature rather than God the Creator of all, and though they shrink from the Gentile name, in order to deceive the unskilful, yet they secretly hold a like sentiment with them. For their subtle saying which they are accustomed to urge, We say not two 'Unoriginates,' they plainly say to deceive the simple; for in their very professing 'We say not two Unoriginates,' they imply two Gods, and these with different natures, one originate and one Unoriginate. And though the Greeks worship one Unoriginate and many originate, but these one Unoriginate and one originate, this is no difference from them; for the God whom they call originate is one out of many, and again the many gods of the Greeks have the same nature with this one, for both he and they are creatures. Unhappy are they, and the more for that their hurt is from thinking against Christ; for they have fallen from the truth, and are greater traitors than the Jews in denying the Christ, and they wallow with the Gentiles, hateful as they are to God, worshipping the creature and many deities. For there is One God, and not many, and One is His Word, and not many; for the Word is God, and He alone has the Form of the Father. Being then such, the Saviour Himself troubled the Jews with these words, 'The Father Himself which has sent Me, has borne witness of Me; you have neither heard His voice at any time nor seen His Form; and you have not His Word abiding in you; for whom He has sent, Him ye believe not.' Suitably has He joined the 'Word' to the 'Form,' to show that the Word of God is Himself Image and Expression and Form of His Father; and that the Jews who did not receive Him who spoke to them, thereby did not receive the Word, which is the Form of God. This too it was that the Patriarch Jacob having seen, received a blessing from Him and the name of Israel instead of Jacob, as divine Scripture witnesses, saying, 'And as he passed by the Form of God, the Sun rose upon him. ' And This it was who said, 'He that has seen Me has seen the Father,' and, 'I in the Father and the Father in Me,' and, 'I and the Father are one;' for thus God is One, and one the faith in the Father and Son; for, though the Word be God, the Lord our God is one Lord; for the Son is proper to that One, and inseparable according to the propriety and peculiarity of His Essence.
17. The Arians, however, not even thus abashed, reply, 'Not as you say, but as we will;' for, whereas you have overthrown our former expedients, we have invented a new one, and it is this:— So are the Son and the Father One, and so is the Father in the Son and the Son in the Father, as we too may become one in Him. For this is written in the Gospel according to John, and Christ desired it for us in these words, 'Holy Father, keep through Your own Name, those whom You have given Me, that they may be one, as We are.' And shortly after; 'Neither pray I for these alone, but for them also which shall believe in Me through their Word; that they all may be one, as Thou, Father, art in Me, and I in You, that they also may be one in Us, that the world may believe that You have sent Me. And the glory which You gave Me I have given them, that they may be one, even as We are one; I in them, and You in Me, that they may be made perfect in one, and that the world may know that You sent Me. ' Then, as having found an evasion, these men of craft add, 'If, as we become one in the Father, so also He and the Father are one, and thus He too is in the Father, how pretend you from His saying, “I and the Father are One,” and “I in the Father and the Father in Me,” that He is proper and like the Father's Essence? For it follows either that we too are proper to the Father's Essence, or He foreign to it, as we are foreign.' Thus they idly babble; but in this their perverseness I see nothing but unreasoning audacity and recklessness from the devil, since it is saying after his pattern, 'We will ascend to heaven, we will be like the Most High.' For what is given to man by grace, this they would make equal to the Godhead of the Giver. Thus hearing that men are called sons, they thought themselves equal to the True Son by nature such. And now again hearing from the Saviour, 'that they may be one as We are,' they deceive themselves, and are arrogant enough to think that they may be such as the Son is in the Father and the Father in the Son; not considering the fall of their 'father the devil,' which happened upon such an imagination.
Source: Four Discourses Against the Arians (New Advent)