Some years ago Michael Card, a contemporary Christian artist, wrote a song called Scandelon. It is about the scandalous nature of the cross. The chorus goes:

He will be the Truth
that will offend them one and all.
A stone that makes men stumble
and a rock that makes them fall.
And many will be broken so that He can make them whole.
And many will be crushed and lose their very soul.

Peter understood the scandalous nature of the cross. It repulsed him. There was no way Jesus was going to go to Jerusalem and be killed. Peter could see Jesus being king and killing others but being king and being killed was not, in his mind, the Messiah's fate.