That man has spoken truly who said: No one takes honor upon himself, except the one who is called by God, for it was our Lord Jesus Christ who called his own disciples before all others to a most glorious apostolate. These holy men became the pillar and mainstay of the truth, and Jesus said that he was sending them just as the Father had sent him.
By these words he is making clear the dignity of the apostolate and the incomparable glory of the power given to them, but he is also, it would seem, giving them a hint about the methods they are to adopt in their apostolic mission. For if Christ thought it necessary to send out his intimate disciples in this fashion, just as the Father had sent him, then surely it was necessary that they whose mission was to be patterned on that of Jesus should see exactly why the Father had sent the Son. And so Christ interpreted the character of his mission to us in a variety of ways. Once he said: I have come to call not the righteous but sinners to repentance. And then at another time he said: I have come down from heaven, not to do my own will, but the will of him who sent me.
For God sent his Son into the world, not to condemn the world, but that the world might be saved through him.
Accordingly, in affirming that they are sent by him just as he was sent by the Father, Christ sums up in a few words the approach they themselves should take to their ministry. From what he said they would gather that it was their vocation to call sinners to repentance, top heal those who were sick whether in body or spirit, to seek in all their dealings never to do their own will but the will of him who sent them, and as far as possible to save the world by their teaching.
Surely it is in all these respects that we find his holy disciples striving to excel. To ascertain this is no great labor; a single reading of the Acts of the Apostles or of Saint Paul's writings is enough."
-- From a commentary on the gospel of John by Saint Cyril of Alexandria (Liturgy of the Hours)