Catena Aurea on John 8:28–30: Augustine of Hippo

And though both are together, yet one is sent, the other sends. For the mission is the incarnation; and the incarnation is of the Son only, not of the Father. He says then, He that sent Me, meaning, By whose Fatherly authority I am made incarnate. The Father however, though He sent the Son, did not withdraw from Him, as He proceeds to say: The Father hath not left Me alone. For it could not be that where He sent the Son, there the Father was not; He who says, I fill heaven and earth. (Jer. 33) And He adds the reason why He did not leave Him: For I do always those things that please Him; always, i. e. not from any particular beginning, but without beginning and without end. For the generation from the Father hath no beginning in time.