He was saying that to deny that the Christ would fulfill His purpose on earth (through death, burial, & ressurection) was a message from Satan.
Thanks. May I offer my interpretation?
I thought the message being given was that Peter was acting like Satan, who tried to put himself ‘in front of’ Jesus and God. I have the feeling that the terms ‘in front of’ and ‘behind me’ were just like the military command chain.
You don’t stand in front of the General, and you don’t tell him his orders are wrong.
Jesus was telling Peter he was acting just like Satan, and should follow God and Jesus instead of thinking he knew better and should decide what happens.
Maybe we are saying the same thing. I don’t understand how it would be a message from Satan, though.