Mark 8:32

And he spake the saying openly. And Peter took him and began to rebuke him.

Openly ... would indicate that Jesus' prophecy of his death and resurrection was made available to the public as well as to the apostles; and, from this, it would seem that Peter was concerned about the erosion of our Lord's popular image that would necessarily result from such a prophecy. It was part of the divine wisdom, however, that all men should know of Jesus' prophecies in this sector. The Pharisees and other leaders were well aware of what he taught in this context, and from their knowledge of it there came the sealing of the tomb and placement of the watch upon our Lord's grave.

And began to rebuke him ... Matthew related the nature of Peter's rebuke: "Be it far from the Lord; this shall never be unto thee" (Matthew 16:22). Thus Peter rejected the idea of the cross; and the fact of Jesus' noblest disciples being opposed to it was a definite temptation to the Lord himself. He said, "Thou art a stumbling block unto me." This shows that some of man's greatest temptations gain access to him through friends and intimates.

And Peter took him ... indicates that Peter probably took our Lord by the hand, or in some other manner led him apart to make this protest. However, the other apostles, as seen in the next verse, had followed and were witnesses of the entire incident.