Catena Aurea on John 17:9–13: Augustine of Hippo

The Son as man kept His disciples in the Father’s name, being placed among them in human form: the Father again kept them in the Son’s name, in that He heard those who asked in the Son’s name. But we must not take this carnally, as if the Father and Son kept us in turns, for the Father, Son, and Holy Ghost guard us at the same time: but Scripture does not raise us, except it stoop to us. Let us understand then that when our Lord says this, He is distinguishing the persons, not dividing the nature, so that when the Son was keeping His disciples by His bodily presence, the Father was waiting to succeed Him on His departure; but both kept them by spiritual power, and when the Son withdrew His bodily presence, He still held with the Father the spiritual keeping. For when the Son as man received them into His keeping, He did not take them from the Father’s keeping, and when the Father gave them into the Son’s keeping, it was to the Son as man, who at the same time was God. Those that Thou gavest Me I have kept, and none of them is lost but the son of perdition; i. e. the betrayer of Christ, predestined to perdition; that the Scripture might be fulfilled, especially the prophecy in Psalm 108.