To bolster the disciples’ wavering faith, vocalized by Thomas (v. 5), Jesus pointed them back to the truth that He is God incarnate. “If you had known Me,” He chided them (the verbs in v. 7 are plurals, indicating that the Lord was no longer addressing Thomas alone as in v. 6, but all the disciples), “you would have known My Father also.” If the disciples had fully grasped who Jesus was, they would have known the Father as well.
The Lord’s statement was nothing less than a claim to full deity and equality with the Father. He is the way to God (v. 6) because He is God. He is not merely a manifestation of God; He is God manifested. That truth, a constant theme in John’s gospel (e.g., 1:1–3, 14, 17, 18; 5:18; 8:58; 10:30–33; 19:7; 20:28–29), is the watershed that divides true from false views of Christ. Many throughout history and today have regarded Jesus as nothing more than a good man; an exemplary, virtuous moral or religious teacher. But that is impossible. No one who claimed to be God incarnate, if his claim were false, could be a good man. If he knew his claim was false, he would be an evil deceiver; if he sincerely believed it was true when it was not, he would be a raving lunatic. But the evidence conclusively shows that Christ was neither a liar nor insane. Rather He was God, exactly as He claimed to be. (For a further defense of this truth, see John MacArthur, John 1–11, The MacArthur New Testament Commentary [Chicago: Moody, 2006], chapters 7, 15, 24.) How each person reacts to Christ’s claim determines his or her eternal destiny (John 8:24).
It is possible to interpret the phrase from now on you know Him, and have seen Him as referring to that very moment in the upper room. However Philip’s question in verse 8, suggesting that the disciples still did not understand Jesus’ point, argues against an immediate fulfillment of His words. It was only after Christ’s death, resurrection, ascension, and the coming of the Spirit at Pentecost (John 14:17, 26; 15:26; 16:13) that the disciples would finally understand Jesus’ deity and relationship to the Father (John 20:28; Acts 2:22ff.; 3:12ff.; 4:8–12; 5:29–32). Because that understanding would certainly come in the future, Jesus spoke of it as if it were a present reality.
14:7 Once more the Lord taught the mysterious union that exists between the Father and Himself. If the disciples had recognized who Jesus really was, they would have known the Father also, because the Lord revealed the Father to men. From now on, and especially after Christ’s resurrection, the disciples would understand that Jesus was God the Son. Then they would realize that to know Christ was to know the Father, and to see the Lord Jesus was to see God. This verse does not teach that God and the Lord Jesus are the same Person. There are three distinct Persons in the Godhead, but there is only one God.
7 Jesus recognized that the ideas held by the disciples about him were less than adequate, so he added, “If you really knew me, you would know my Father as well.” Throughout his ministry, Jesus had taught his followers that he had come to do the will of his Father and to carry out what the Father had planned. So perfect was the correspondence between the life of Jesus and the will of God that to know Jesus was to know his Father too. As a perfect Son, Jesus revealed with total accuracy the person of the Father. Anticipating the events about to take place, Jesus can say, “From now on, you do know him and have seen him.”
 MacArthur, J. F., Jr. (2008). John 12–21 (p. 104). Chicago, IL: Moody Publishers.
 MacDonald, W. (1995). Believer’s Bible Commentary: Old and New Testaments. (A. Farstad, Ed.) (p. 1546). Nashville: Thomas Nelson.
 Mounce, R. H. (2007). John. In T. Longman III & D. E. Garland (Eds.), The Expositor’s Bible Commentary: Luke–Acts (Revised Edition) (Vol. 10, p. 561). Grand Rapids, MI: Zondervan.