Matthew 16:22

‘And Peter took him aside, and began to rebuke him, saying, “Be it far from you, Lord, this will never happen to you.” '

At Jesus' words about rejection by the Jewish leaders resulting in His death Peter felt a need to intervene. He was probably still glowing at Jesus' previous commendation of him. Now he felt that Jesus was becoming too pessimistic, and that that could only put disciples off. And he might also have found the idea too much to bear. So he ‘took Him aside' and began to rebuke Him, telling Him that that could never happen to Him, that He was distorting the position. How much of this was due to self-opinionation and how much to an excess of sensitivity we do not know, but it produced an instant reaction from Jesus. The words He was hearing from a beloved disciple were not helping Him. And Peter had to learn to seek the mind of Heaven before he spoke. Jesus' words were not just a rebuke to Peter. They were intended to pull him up short and make him think of the consequences of what he was saying before he spoke.

The rebuke, and the public nature of it, were very necessary. Peter had been held up as an example of one to whom God revealed things. It was therefore necessary that he and the disciples recognise that there was someone else who could reveal things to him as well.