John Chrysostom

"As Thou hast sent Me into the world, even so have I also sent them into the world." As Paul also saith, "Having put in us the word of reconciliation." For the same end for which Christ came, for the same did these take possession of the world. In this place again the "as" is not put to signify resemblance in the case of Himself and the Apostles; for how was it possible for men to be sent otherwise? But it was His custom to speak of the future as having come to pass.

Homily on the Gospel of John 82 ↗

Theophylact of Ohrid

He adds: "As You sent Me into the world... and for them I consecrate Myself," that is, I offer Myself as a sacrifice; so sanctify them also, that is, set them apart as a sacrifice for the sake of preaching and appoint them as witnesses of the truth, just as You also sent Me as a witness of the truth and as a sacrifice. For everything offered as a sacrifice is called holy. …

Commentary on John ↗

Augustine of Hippo

But now He still goes on to speak of the apostles, for He proceeds to add, "As Thou hast sent me into the world, even so have I also sent them into the world." Whom did He so send but His apostles? For even the very name of apostles, which is a Greek word, signifies in Latin nothing more than, those that are sent. God, therefore, sent His Son, not in sinful flesh, but in the likeness of sinful flesh; and His Son sent those who, born themselves in sinful flesh, were sanctified by Him from the defilement of sin.

Tractates on John 108 ↗

Thomas Aquinas

The need for their sanctification is added when he says, as you did send me into the world, so I have sent them into the world. He is saying in effect: I have come to preach the truth: "For this I was born... to bear witness to the truth" (18:37). And so I have sent my disciples to preach the truth: "Go into all the world and preach the gospel to the whole creation" (Mk 16:15). Accordingly, they have to be sanctified in the truth: "As the Father has sent me, even so I send you" (20:21).

Commentary on John ↗

Bonaventure

As you sent me. Here the third point is touched upon, namely the reason for being heard, which is twofold, namely the office committed to them and the sacrifice offered for them. By reason of the office committed to them, they ought to be preserved and sanctified, because they were sent among the wicked: therefore he says: As you sent me into the world, to suffering; so also I have sent them into the world, namely to suffer: whence Matthew 10: "Behold, I send you as sheep in the midst of wolves." Therefore by reason of the office it …

Commentary on John, Chapter 17 ↗