Mark 8:30

And he charged them
His disciples, after he had declared his approbation of Peter's confession of faith, and signified he would build his church on that rock, and the gates of hell should not prevail against it: and promised Peter the keys of the kingdom of heaven; and that whatsoever was bound, or loosed by him on earth, should be bound and loosed in heaven; which are omitted by Mark, but related by Matthew, ( Matthew 16:17-19 ) : after this he gave a strict and severe charge,

that they should tell no man of him;
that he was the Messiah, and the Son of God; (See Gill on Matthew 16:20).