33 The Lord has not left in doubt or obscurity the teaching conveyed in this great mystery; He has not abandoned us to lose our way in dim uncertainty. Listen to Him as He reveals the full knowledge of this faith to His Apostles;— I am the Way and the Truth and the Life; no man comes unto the Father but through Me. If you know Me, you know My Father also; and from henceforth you shall know Him, and have seen Him. Philip says unto Him, Lord, show us the Father, and it suffices us.
Jesus says unto him, Have I been so long time with you, and you have not known Me, Philip? He that has seen Me has seen the Father also. How do you say, Show us the Father? Do you not believe Me, that I am in the Father, and the Father is in Me? The words that I speak unto you I speak not of Myself, but the Father that dwells in Me, He does His works. Believe Me, that I am in the Father, and the Father in Me; or else believe for the very works' sake</em>. He Who is the Way leads us not into by-paths or trackless wastes: He Who is the Truth mocks us not with lies; He Who is the Life betrays us not into delusions which are death.
He Himself has chosen these winning names to indicate the methods which He has appointed for our salvation. As the Way, He will guide us to the Truth; the Truth will establish us in the Life. And therefore it is all-important for us to know what is the mysterious mode, which He reveals, of attaining this life. No man comes to the Father but through Me. The way to the Father is through the Son. And now we must enquire whether this is to be by a course of obedience to His teaching, or by faith in His Godhead.
For it is conceivable that our way to the Father may be through adherence to the Son's teaching, rather than through believing that the Godhead of the Father dwells in the Son. And therefore let us, in the next place, seek out the true meaning of the instruction given us here. For it is not by cleaving to a preconceived opinion, but by studying the force of the words, that we shall enter into possession of this faith.
Source: On the Trinity (New Advent)