Luke 9:20,21 He said unto them, But whom say ye that I am? Peter answering said, The Christ [Messiah] of God. 21 And he straitly charged them, and commanded them to tell no man that thing;
They were not to tell anyone directly that he was the Messiah. If they had preached Jesus himself as the Messiah at that time it would have been premature because his work on the cross was not yet fulfilled. This is confirmed by the following verse:
Luke 9:22 Saying, The Son of man must suffer many things, and be rejected of the elders and chief priests and scribes, and be slain, and be raised the third day.
After that, his Messiahship would be confirmed and it would be right to identify him as the Messiah – the Christ:
Romans 1:3,4 Concerning his Son Jesus Christ our Lord, which was made of the seed of David according to the flesh; 4 And declared to be the Son of God with power, according to the spirit of holiness, by the resurrection from the dead:
I hope you have found this helpful.