Luke 9:19 Meaning

17And they did eat, and were all filled: and there was taken up of fragments that remained to them twelve baskets.

18And it came to pass, as he was alone praying, his disciples were with him: and he asked them, saying, Whom say the people that I am?

19They answering said, John the Baptist; but some say, Elias; and others say, that one of the old prophets is risen again.

20He said unto them, But whom say ye that I am? Peter answering said, The Christ of God.

21And he straitly charged them, and commanded them to tell no man that thing;