Note 1 at Mt 26:33: There are only sixteen instances in the Gospels that are common to all four Gospel writers and only nine common instances outside of the crucifixion events, and this prophecy of Peter’s denial is one of them. For the Lord to inspire the repetition of an event like this, there must be a special significance to it.

One of the points that the Lord must be stressing is that we are nothing without Him (Joh 15:4-5). Peter went on to become probably the best known of the twelve apostles. He was used mightily of the Lord. But the Lord didn't want him or us to forget that it was Christ in Peter (Ga 2:20) and not Peter himself who was great. This incident illustrates what Peter was capable of on his own.

This also shows that the Lord has never had anyone who was qualified working for Him yet. Peter wasn't qualified and, even at our best, neither are we. If we realize that we are nothing and have nothing, then we are prime candidates to be used of God (1Co 1:26-29).

This also illustrates the extent of our Father's love and forgiveness. If God not only forgave Peter for this sin but also reinstated and advanced him, then surely we have not pushed God's grace beyond its limit. Where sin abounds, grace much more abounds (Ro 5:20).