But I have prayed for thee, that thy faith fail not. The prayer of Satan apparently was not refused. Jesus, however, says, that for one of that loved company, who he knew from his peculiar temperament was in especial peril, he had prayed.
The prayer was answered thus: the temptation came to all the apostles; all fell; Peter, though, more disastrously by far than his brethren, but the result of the fall was not hopeless despair as in the case of Judas, but bitter remorse and a brave manly repentance.
"It is said by Roman divines (e.g. Maldonatus, a Lapide, and Mai, here) that this prayer and precept of our Lord extends to all bishops of Rome as St. Peter's successors, and that in speaking to St. Peter our Lord spoke to them.
Would they be willing to complete the parallel, and say that the bishops of Rome specially need prayer, because they deny Christ? Let them not take a part of it and leave the rest" (Bishop Wordsworth).
When thou art converted. "Converted" must not be understood here in its technical sense; it should rather be translated, "And thou, when thou hast turned (i.e. to God) strengthen thy brethren."