What else does the Lord’s passion present us with in our head, but supremely the tests and trials of this life? That is why, as the time of his death drew near, Christ said to Peter, “Satan has asked for you all to sift you like wheat. And I have prayed, Peter, for you, that your faith should not fall. Go and strengthen your brothers” (v. 31–32).
Peter certainly has strengthened us by his apostolate, martyrdom, and letters. In them he also instructed us to be carefully vigilant, having the consolation of prophecy like a light in the night. “We have,” he said, “the more certain prophetic word, to which you do well to attend, as to a lamp shining in a dark place, until the day dawns, and the morning star rises in your heart” (2 Peter 1:19).
-Augustine, Sermon 210:6