After having asked that the Apostles be kept in love, Our Lord asked His Father that they be kept from evil. He said that He was leaving the world, but they were to stay in it, even though the world would hate them as the world would crucify Him. They, and all who would be united with Him through this apostolic body, were to be in the world, but not of it. Our Lord did not ask His Father that they be preserved from sickness, mock trials, false charges; He asked only that they be kept from sin. Material assault from without must be met by spiritual resistance from within. Since they were to be ridiculed by the world, He was asking that they bear up under it for His sake. There was to be no escapism. The world would say, “If you embrace Christ, you are an escapist.” But Christ said that if we escape Him, we are escapists. He gave the death blow to the charge that His religion was an escape. On the Mount of Beatitudes He told His followers to count themselves happy if they were persecuted; now He told them they must share the hatred of Him. The Cross is no “escape” it is a burden—a “yoke that is sweet and a burden that is light.”
To live in the midst of the infection of the world and at the same time to be immunized from it is something that is impossible without grace. The Father was now asked to keep them holy:

I am not asking that Thou shouldst take them Out of the world, but that
Thou shouldst keep them clear of what is evil… Keep them holy, then, through the truth;
It is Thy word that is truth. John 17:15-17

– from Life of Christ (1958)