Jesus told Peter, “The cock will not crow before you deny me three times.” St. Luke, in his Gospel gives a fuller presentation of that scene. Let me quote what he recalls Jesus saying.
“Simon, Simon, behold Satan has demanded to sift all of you like wheat, but I have prayed that your own faith may not fail, and once you have turned back, you must strengthen our brethren.”
Let me tell you, that as a seventeen-year-old seminarian I was very happy to come on that verse. A severe seminary professor had told us that any boy who had committed a mortal sin should not present himself for ordination to the priesthood. Now, since boys will be boys, I was thinking I might have committed a mortal sin, and I was wondering if I should give up studying to be a priest.
Then, I came on that passage from Luke. In it Jesus said he knew that Peter was going to deny him three times; but even so, he had forgiven him in advance, and he had great work in store for Peter after he repented.
On reading what Luke quoted Jesus as saying I recalled that old expression, “God know the clay of which we are made.” I was comforted by knowing that God makes allowances for our weakness, and he does not give up on us after we slip.