Theophylact of Ohrid
Catena Aurea · Johannesevangelium 8
Then said the Jews unto him, Now we know that thou hast a devil. Abraham is dead, and the prophets; and thou sayest, If a man keep my saying, he shall never taste of death. Art thou greater than our father Abraham, which is dead? and the prophets are dead; whom makest thou thyself? Jesus answered, If I honour myself, my honour is nothing; it is my Father that honoureth me; of whom ye say, that he is your God: Yet ye have not known him; but I know him: and if I should say, I know him not, I shall be a liar like unto you: but I know him, and keep his saying. Your father Abraham rejoiced to see my day: and he saw it, and was glad.
Having that knowledge by nature; for as I am, so is the Father also; I know Myself, and therefore I know Him. And He gives the proof that He knows Him: And I keep His saying, i. e. His commandments. Some understand, I keep His saying, to mean, I keep the nature of His substance unchanged; for the substance of the Father and the Son is the same, as their nature is the same; and therefore I know the Father. And here has the force of because: I know Him because I keep His saying.