Matthew 16:21 – 23

21 From that time Jesus began to show to His disciples that He must go to Jerusalem, and suffer many things from the elders and chief priests and scribes, and be killed, and be raised the third day.

22 Then Peter took Him aside and began to rebuke Him, saying, “Far be it from You, Lord; this shall not happen to You!”

23 But He turned and said to Peter, “Get behind Me, Satan! You are an offense to Me, for you are not mindful of the things of God, but the things of men.”

Jesus is preparing these men for the near future, when He does go to Jerusalem and is arrested by the Jews and turned over to the Romans to be executed for crimes He is innocent of. He is also preparing them for His resurrection which is proof of who He truly is.

These men had worked very closely with Jesus for the three years of His public ministry. His arrest, torture, and death would cause them much grief. Peter was always the one who was outspoken. His impulsive speech in Jesus defense was not surprising given we know he drew his sword and attempted to use it at the time of Jesus arrest in the garden.(John 18:10) He was willing to do his part to prevent what he saw as a tragedy.

When Jesus calls Peter, “Satan” he is using the primary meaning of the name, which is “adversary.” Peter's call to attempt to stop Jesus from being crucified meant he was going against the plan of salvation which had been in the works since before the foundation of the world. Even with his good intentions, he was going against the plan and was an adversary of Jesus finishing the plan of salvation and initiating the kingdom. Peter's desire was for an earthly kingdom as many of the Jews believed the Messiah would be the king of. If the king were dead there would be no kingdom. This why Jesus told Peter his mind was on the things of men and not the things of God.