JOHN 14:7 (LUTHER)

7. If you had known Me, you would have known My Father also; henceforth you know Him and have seen Him.

Here the Lord Christ again uses a new parable and symbolic speech before His disciples, to prompt them to begin asking about His Father, who and where He is. For although He has spoken about this very plainly and has revealed that He is the Way, the Truth, and the Life, by saying: “No one comes to the Father but by Me,” the disciples still do not understand. They hear these words about the Way, the Truth, and the Life, about coming to the Father, etc., with their reason and their carnal mind alone, and cannot make sense of them. Therefore Christ good-naturedly lets them blunder along. He throws a block in their way, to jolt them and make them ask more questions. He begins by saying: “If you had known Me, etc.” What? Do they not know Christ? Do they not hear His voice, and do they not see Him before their very eyes? Did they not travel about with Him for a long time? This bears out my earlier statement32 that knowing Christ is not identical here with seeing Him face to face and, as St. Paul says, knowing Him after the flesh (2 Cor. 5:16). No, it means to know how to regard Him, to know what we possess in Him and how to avail ourselves of Him.
He means, in brief, that all depends on this, and that it must be a Christian’s true knowledge to learn to know Christ aright, to distinguish Him from all thought, existence, doctrine, life, and all that man may undertake, to cling to Him alone in faith, and to say wholeheartedly: “I know and want to know nothing in divine matters save my Lord Christ: He alone must be everything that concerns my salvation and that must be settled between God and me. And though I experience many trials and much opposition on the part of the devil, the world, and my own conscience, and must suffer even death because of this, I will still take my stand here. I am determined to live and to die in this faith.” “This,” Christ says, “is knowing Me aright, and through Me also knowing the Father.”
“But if you look at Me as a cow looks at a new gate, if you merely see Me going along in the greatest weakness, letting Myself be so shamefully crucified, killed, and buried, then you cannot see or believe that I am the Way, the Truth, and the Life, and that you must come to the Father through Me alone. No, then you will believe the opposite of Me, like the Jewish people, who consider Me to be error and deception, sheer lies and dreams, yes, nothing but death and the venom of hell. Therefore if you want to know Me aright, you must not follow your eyes and carnal understanding, like the Jews; but you must grasp the words which you hear from Me in your hearts, cling to them, and be guided by them alone. Then you will experience how I go through weakness, cross, death, and everything, and in this way come to the Father; and I will draw you on the same way with Me and through Me if you remain loyal to Me in death and every need, through faith in these words.”
This is what Christ means when He says: “If you had known Me, you would have known My Father.” As though He were saying: “Why do you continue to think and worry about where I am going, about the way, or about what and where the Father is to whom I am going? Do you not hear? If you have Me, you have everything; and if you hear My words, though you still grasp and hold them imperfectly, you know Me. And inasmuch as you know Me, you know the Father also and have already seen Him.” Christ will now explain and expand this further. For, as I have said, these words are merely an introduction to a new sermon on how the Father is to be known in Him.
Luther, M. (1999, c1961). Vol. 24: Luther's works, vol. 24 : Sermons on the Gospel of St. John: Chapters 14-16 (J. J. Pelikan, H. C. Oswald & H. T. Lehmann, Ed.). Luther's Works (24:54). Saint Louis: Concordia Publishing House.