Matthew 16:23

‘But he turned, and said to Peter, “Get you behind me, Satan, You are a snare to me, for you do not mind the things of God, but the things of men.” '

So He turned to Peter, and naming Him as Satan ‘the adversary' (satanas), bade him get behind Him, pointing out that he was becoming a snare or stumblingblock to Him (literally the trigger (skandalon) that makes the trap work) in seeking to turn Him aside from His destiny as the Servant of the Lord. He pointed out that what he was saying was not minding what God wanted, it was simply thinking like men did who had no part in the things of God.

Note here how quickly Peter the rock-like man had rather become a rock of stumbling through failing to mind the things of God, and how the one blessed of the Father with enlightenment was now listening to Satan in the darkness. It was a reminder that he could not effectively use his keys, nor his power to bind and loose, until he had learned to discover the mind of God. And at present that was not so. He was behaving like Satan who had also tempted Him to take the easy way (Matthew 4:1). Jesus was ever aware that Satan still sought to divert Him from God's chosen path, and He saw him at work through Peter.