This is one of the seven great "I AM's" of John's gospel. "I am the BREAD OF LIFE," "I am the LIGHT OF THE WORLD," "I am the DOOR," I am the GOOD SHEPHERD," "I am the RESURRECTION AND THE LIFE," "I am the TRUE VINE," and "I am the WAY, the TRUTH, and the LIFE."
He is saying to His disciples that He is THE WAY to God. He does not merely show us the way by example, He is not merely a prophet to teach us the way, nor does He merely guide us in the way by strong assistance. HE IS HIMSELF THE WAY! He is the way from God to men in that all heavenly blessings come through the Son. He is the way from men to God in that He is our righteousness and our sin-offering. He enables God to be both just and the justifier of sinners who believe.
He is THE TRUTH. He is not only the true God and true man, but HE IS TRUTH ITSELF! He is the sum and substance of all the truth of the gospel, of all the promises, of all the types and shadows; and he is the true way in opposition to every false way. Pilate asked, "What is truth?" Our Lord answers that question here in John 14, "I AM THE TRUTH."
He is THE LIFE. Christ speaks of life as opposed to death--all death and all kinds of death. He has life in Himself. He is the source and giver of life. He is the light of life, the word of life, and He came that we might have life. "He that hath the Son of God hath life; and he that hath not the Son of God hath not life" (I John 5:12).