3 Why, then, Philip, do you say, “Show us the Father, and it suffices us? Have I been so long time with you, and yet have ye not known me, Philip? He that sees me, sees the Father also.” If it interests you much to see this, believe at least what you see not. For “how,” He says, “do you say, Show us the Father?” If you have seen me, who am His perfect likeness, you have seen Him to whom I am like. And if you can not directly see this, “do you not believe,” at least, “that I am in the Father, and the Father in me?”
But Philip might say here, “I see You indeed, and believe Your full likeness to the Father; but is one to be reproved and rebuked because, when he sees one who bears a likeness to another, he wishes to see that other to whom he is like? I know, indeed, the image, but as yet I know only the one without the other; it is not enough for me, unless I know that other whose likeness he bears. Show us, therefore, the Father, and it suffices us.” But the Master really reproved the disciple because He saw into the heart of his questioner.
For it was with the idea, as if the Father were somehow better than the Son, that Philip had the desire to know the Father: and so he did not even know the Son, because believing that He was inferior to another. It was to correct such a notion that it was said, “He that sees me, sees the Father also. How do you say, Show us the Father?” I see the meaning of your words: it is not the original likeness you seek to see, but it is that other you think the superior. “Do you not believe that I am in the Father, and the Father in me?”
Why do you desire to dis cover some distance between those who are thus alike? Why do you crave the separate knowledge of those who cannot be separated? What, after this, He says not only to Philip, but to all of them together, must not now be thrust into a corner, in order that, by His help, it may be the more carefully expounded.
Source: Tractates on the Gospel of John (New Advent)