Jesus explained to Peter--who really would have rather heard something else--that being a messiah included rejection and suffering.
Long before their conversation, the prophet Isaiah told what it is like to be God's servant and what God's servant is to be like.
"Every day I listen to God. I pay attention to God not to those who oppose me. My call is to help the weary and to ignore those who oppose me."
Isaiah reminds us that when we accept God's help and prompting, we can together overcome our adversaries.