5 But when He added, “And the saying which you have heard is not mine, but the Father's who sent me,” let us not be filled with wonder or fear: He is not inferior to the Father, and yet He is not, save of the Father: He is not unequal in Himself, but He is not of Himself. For it was no false word He uttered when He said, “He that loves me not, keeps not my sayings.” He called them, you see, His own sayings; does He, then, contradict Himself when He said again, “And the saying which you have heard is not mine”?
And, perhaps, it was on account of some intended distinction that, when He said His own, He used “sayings” in the plural; but when He said that “the saying,” that is, the Word, was not His own, but the Father's, He wished it to be understood of Himself. For in the beginning was the Word, and the Word was with God, and the Word was God. For as the Word, He is certainly not His own, but the Father's: just as He is not His own image, but the Father's; and is not Himself His own Son, but the Father's. Rightly, therefore, does He attribute whatever He does, as equal, to the Author of all, of whom He has this very prerogative, that He is in all respects His equal.
Source: Tractates on the Gospel of John (New Advent)