Albert Barnes Commentary John 14:7

"If ye had known me, ye would have known my Father also: from henceforth ye know him, and have seen him." — John 14:7 (ASV)

If you had known me. By this Jesus does not intend to say that they were not truly his disciples, but that they had not a full and accurate knowledge of his character and designs. They still retained, to a large extent, the Jewish notions concerning a temporal Messiah, and did not fully understand that he was to die and be raised from the dead.

You should have known my Father also. You would have known the counsels and designs of my Father concerning my death and resurrection. If you had been divested of your Jewish prejudices about the Messiah, if you had understood that it was proper for me to die, you would also have understood the purposes and plans of God in my death; and, knowing that, you would have seen that it was wise and best. We see here that a correct knowledge of the character and work of Christ is the same as a correct knowledge of the counsels and plans of God; and we see, also, that the reasons why we do not have such a knowledge are our previous prejudices and erroneous views.

From henceforth. From this time. From my death and resurrection you will understand the plans and counsels of God.

You know him. You will have just views of his plans and designs.

Have seen him. That is, they had seen Jesus Christ, his image, and the brightness of his glory (Hebrews 1:3), which was the same as having seen the Father (John 14:9).