9 And what do they follow, who have been loosed and raised up, but the Light from which they hear, “I am the light of the world: he that follows me shall not walk in darkness”? For the Lord gives light to the blind. Therefore we, brethren, having the eye-salve of faith, are now enlightened. For His spittle did before mingle with the earth, by which the eyes of him who was born blind were anointed. We, too, have been born blind of Adam, and have need of Him to enlighten us.
He mixed spittle with clay: “The Word was made flesh, and dwelt among us.” He mixed spittle with earth; hence it was predicted, “Truth has sprung from the earth;” and He said Himself, “I am the way, the truth, and the life.” When we shall see face to face, we shall have the full fruition of the truth; for this also is promised to us. For who would dare hope for what God had not deigned either to promise or to give? We shall see face to face. The apostle says, “Now I know in part, now through a glass darkly; but then, face to face.” And the Apostle John says in his epistle, “Beloved, now are we the sons of God; and it has not yet appeared what we shall be: we know that, when He shall appear, we shall be like Him; for we shall see Him even as He is.” This is a great promise; if you love, follow.
I do love, do you say, but by what way am I to follow? If the Lord your God had said to you, “I am the truth and the life,” in desiring truth and longing for life, you might truly ask the way by which you might come to these, and might say to yourself: A great thing is the truth, a great thing is the life, were there only the means whereby my soul might come thereto! Do you ask by what way? Hear Him say at the first, “I am the way.” Before He said whither, He premised by what way: “I am,” says He, “the way.”
The way whither? “And the truth and the life.” First, He told you the way to come; then, whither to come. I am the way, I am the truth, I am the life. Remaining with the Father, the truth and life; putting on flesh, He became the way. It is not said to you, Labor in finding a way to come to the truth and life; this is not said to you. Sluggard, arise: the way itself has come to you, and roused you from your sleep; if, however, it has roused you, up and walk. Perhaps you are trying to walk, and art not able, because your feet ache. How come your feet to ache? Have they been running over rough places at the bidding of avarice? But the word of God has healed even the lame. Behold, you say, I have my feet sound, but the way itself I see not. He has also enlightened the blind.
Source: Tractates on the Gospel of John (New Advent)