Peter knew that the only way to be right with God was through faith in the life, death and resurrection of Jesus. It is the message he worked so hard to get to the Jews that they might believe and have life.
But Peter was also tempted to believe that being Jewish or acting Jewish had a little more street cred than not being Jewish.
It's easy to do.
I do it.
I sometimes get sucked up into the surface of things and forget the substance of things and I have to constantly be reminded of the simple truth of Jesus solely, Jesus wholly, Jesus ever only be.
It is good to be surrounded by God-fearing, Gospel-filled friends who can point this out, like Paul did for Peter, when we accidentally add to or take away from the only thing that saves: Jesus all by Himself.