12 But the disciples, still thinking that the Father is something greater than the Son, seeing only the flesh, and not understanding His divinity, said to Him, “Lord, show us the Father and it suffices us.” As much as to say, “We know You already, and bless You that we know You: for we thank You that You have shown Yourself to us. But as yet we know not the Father: therefore our heart is inflamed, and occupied with a certain holy longing of seeing Your Father who sent You.
Show us Him, and we shall desire nothing more of You: for it suffices us when He has been shown, than whom none can be greater.” A good longing, a good desire; but small intelligence. Now the Lord Jesus Himself, regarding them as small men seeking great things, and Himself great among the small, and yet small among the small, says to Philip, one of the disciples, who had said this: “Am I so long time with you, and you have not known me, Philip?” Here Philip might have answered, You we have known, but did we say to You, Show us Yourself?
We have known You, but it is the Father we seek to know. He immediately adds, “He that has seen me, has seen the Father also.” If, then, One equal with the Father has been sent, let us not estimate Him from the weakness of the flesh, but think of the majesty clothed in flesh, but not weighed down by the flesh. For, remaining God with the Father, He was made man among men, that, through Him who was made man, you might become such as to receive God. For man could not receive God.
Man could see man; God he could not apprehend. Why could he not apprehend God? Because he had not the eye of the heart, by which to apprehend Him. There was something within disordered, something without sound: man had the eyes of the body sound, but the eyes of the heart sick. He was made man to the eye of the body; so that, believing on Him who could be seen in bodily form, you might be healed for seeing Him whom you were not able to see spiritually. “Am I so long time with you, and you know me not, Philip?
He that has seen me, has seen the Father also.” Why did they not see Him? Lo, they did see Him, and yet saw not the Father: they saw the flesh, but the majesty was concealed. What the disciples who loved Him saw, saw also the Jews who crucified Him. Inwardly, then, was He all; and in such manner inwardly in the flesh, that He remained with the Father when He came to the flesh.
Source: Tractates on the Gospel of John (New Advent)