He said to them, “But who do you say that I am?” Peter answered and said to Him, “You are the Christ.” Then He strictly warned them that they should tell no one about Him. And He began to teach them that the Son of Man must suffer many things, and be rejected by the elders and chief priests and scribes, and be killed, and after three days rise again. He spoke this word openly. And Peter took Him aside and began to rebuke Him. But when He had turned around and looked at His disciples, He rebuked Peter, saying, “Get behind Me, Satan! For you are not mindful of the things of God, but the things of men.” (Mar 8:29-33 NKJ)
There was the Christ, and then there was The Christ. Peter’s Christ was going to restore the Kingdom of Israel and remove the Romans. There would be a new king in the land and perhaps a position there for me (Peter). However, the Kingdom Jesus was going to usher in was the Kingdom of God, but first, he would have to go to the cross.
Peter takes Jesus aside to tell him his plan and rebukes him. Jesus, seeing how Peter wanted to settle for the natural rebukes the author of this failed plan—Satan himself. Peter wasn’t demon possessed, but he was listening to the wrong source. Hearing from God? Test the spirit to make sure you’re hearing from the right source.
Beloved, do not believe every spirit, but test the spirits, whether they are of God; because many false prophets have gone out into the world. By this you know the Spirit of God: Every spirit that confesses that Jesus Christ has come in the flesh is of God, and every spirit that does not confess that Jesus Christ has come in the flesh is not of God. (1Jo 4:1-3 NKJ)