It is one thing for a student to disagree with his teacher. But it is another thing entirely for a student to rebuke his teacher for his teaching. Yet, that is precisely what the Apostle Peter did. He had the gall to confront the incarnate Word of God, the One who embodies all truth, and rebuke Him for what He was teaching (Mark 8:32).
To make matters worse, the Greek word translated as "rebuke" is used biblically in connection with the condemnation of demons. When Jesus silenced demons, He did it by rebuking them, judging them worthy of condemnation (Matt. 17:18; Mark 1:25; 9:25; Luke 4:35; 9:42). It is clear that Peter's protest was not mild; he stood up to Jesus with the full measure of hostility. The Apostle who had said, "You are the Christ, the Son of the living God," and who had heard Jesus say, "Blessed are you, Simon Bar- Jonah" (Matt. 16:16–17a), presumed to correct and admonish his Master.