Augustine of Hippo
Catena Aurea · Johannesevangelium 17
I have given them thy word; and the world hath hated them, because they are not of the world, even as I am not of the world. I pray not that thou shouldest take them out of the world, but that thou shouldest keep them from the evil. They are not of the world, even as I am not of the world. Sanctify them through thy truth; thy word is truth. As thou hast sent me into the world, even so have I also sent them into the world. And for their sakes I sanctify myself, that they also might be sanctified through the truth.
(Tr. cviii) It is manifest by this, that He is still speaking of the Apostles; for the very word Apostle means in the Greek, sent. But since they are His members, in that He is the Head of the Church, He says, And for their sakes I sanctify Myself; i. e. I in Myself sanctify them, since they are Myself. And to make it more clear that this was His meaning, He adds, That they also might be sanctified through the truth, i. e. in Me; inasmuch as the Word is truth, in which the Son of man was sanctified from the time that the Word was made flesh. For then He sanctified Himself in Himself, i. e. Himself as man, in Himself as the Word: the Word and man being one Christ. But of His members it is that He saith, And for their sakes I sanctify Myself, i. e. them in Me, since in Me both they and I are. That they also might be sanctified in truth: they also, i. e. even as Myself; and in the truth, i. e. Myself.