Why Did Jesus Call Peter “Satan” in the Gospels?

"Retro mihi Satanas". Peter had implied tht the Messias had not come to suffer, which, of course, Christ knew all along was God's plan for His Son.

From Aleteia

By Philip Kosloski

In what is arguably Jesus' harshest rebuke, Jesus equates Peter with Satan, a rebellious angel who rejected God's plan for the world.

Every word Jesus spoke was deliberate, choosing precisely the correct word to use at the exact right time. He wasn't someone who overreacted or let a word slip out of his mouth without thinking.

That's why Jesus' use of the word "Satan" to describe Peter should shock us. Jesus didn't say it by accident; he meant to call out the lie that Peter was speaking.

Letting God lead the way

What prompted Jesus to use such a harsh rebuke was Peter's disbelief that the Messiah was called to suffer:

Jesus began to show his disciples
that he must go to Jerusalem and suffer greatly
from the elders, the chief priests, and the scribes,
and be killed and on the third day be raised.
Then Peter took Jesus aside and began to rebuke him,
"God forbid, Lord! No such thing shall ever happen to you." (Matthew 16:21-22)

This rebuke of Peter's elicited an even greater rebuke from Jesus:

He turned and said to Peter,
"Get behind me, Satan! You are an obstacle to me. 
You are thinking not as God does, but as human beings do." (Matthew 16:23)

Pope Benedict XVI reflected on this passage during a general audience, explaining why Jesus rebuked Peter so sternly:

Jesus' answer demolished all his false expectations, calling him to conversion and to follow him... [Jesus was saying to Peter] It is not for you to show me the way; I take my own way and you should follow me.

Peter was thinking like Satan, a rebellious angel who did not want to follow God's will, but wanted to do his own thing. Satan believed his way was the best and did not want to obey God.

This is evident in Jesus' encounter with Satan in the desert and the various temptations that were offered. The first temptation Satan offered was a way out of the suffering Jesus was experiencing.

Jesus was hungry and Satan said to him, "If you are the Son of God, command these stones to become loaves of bread" (Matthew 4:3)

Or in Peter's words, "God forbid, Lord! No such thing shall ever happen to you." Peter was thinking like Satan in the desert, offering an alternative path that would take Jesus away from suffering. Its essentially not trusting that God knows what he is doing and thinking that you have a better idea.

Pope Benedict XVI concluded his reflection by saying, "God chooses a different way. God chooses the way of the transformation of hearts in suffering and in humility. And we, like Peter, must convert, over and over again. We must follow Jesus and not go before him:  it is he who shows us the way."