It is surely no coincidence that both instances appear in the same passage. The inspired writer is ramming home how quickly and easily a sincere believer can slip from attaining such spiritual revelation as to win Jesus’ high praise to being the devil’s mouthpiece.

Matthew 16:17-23 Jesus answered him, “Blessed are you, Simon Bar Jonah, for flesh and blood has not revealed this to you, but my Father who is in heaven. I also tell you that you are Peter, and on this rock I will build my assembly, and the gates of Hades will not prevail against it. I will give to you the keys of the Kingdom of Heaven . . .” From that time, Jesus began to show his disciples that he must go to Jerusalem and suffer many things from the elders, chief priests, and scribes, and be killed, and the third day be raised up. Peter took him aside, and began to rebuke him, saying, “Far be it from you, Lord! This will never be done to you.” But he turned, and said to Peter, “Get behind me, Satan! You are a stumbling block to me, for you are not setting your mind on the things of God, but on the things of men.”

(Emphasis mine.)