3 What sees the Father, or rather, what does the Son see in the Father, that Himself also may do? Perhaps I may be able to speak it, but show me the man who can comprehend it; or perhaps I may be able to think and not speak it; or perhaps I may not be able even to think it. For that divinity excels us, as God excels men, as the immortal excels a mortal, as the eternal excels the temporal. May He inspire and endow us, and out of that fountain of life deign to bedew and to drop somewhat on our thirst, that we may not be parched in this wilderness!
Let us say to Him, Lord, to whom we have learned to say Father. We make bold to say this, because Himself willed it; if only we so live that He may not say to us, “If I am a Father, where is mine honor? If I am Lord, where is my fear?” Let us then say to Him, “Our Father.” To whom do we say, “Our Father”? To the Father of Christ. He, then, who says “Our Father” to the Father of Christ, says to Christ, what else but “Our Brother”? Not, however, as He is the Father of Christ is He in like manner our Father; for Christ never so conjoined us as to make no distinction between Him and us.
For He is the Son equal to the Father, the eternal Son with the Father, and co-eternal with the Father; but we became sons through the Son, adopted through the Only-begotten. Hence was it never heard from the mouth of our Lord Jesus Christ, when speaking to His disciples, that He said of the supreme God His Father, “Our Father;” but He said either “My Father” or “Your Father.” But He said not “Our Father;” so much so, that in a certain place He used these two expressions: “I go to my God,” says He, “and to your God.” Why did He not say, “Our God”? Further, He said, “My Father, and your Father;” He said not, “Our Father.” He so joins as to distinguish, distinguishes so as not to disjoin. He wills us to be one in Him, but the Father and Himself one.
Source: Tractates on the Gospel of John (New Advent)