Luke 9:21

But he forcefully commanded ¹  them not to tell this to anyone, ² 

Jesus strictly warned them not to tell this to anyone.

But He warned them and instructed them not to tell this to anyone,

Jesus warned them not to tell anyone about this.

Jesus then warned them to keep it quiet. They were to tell no one what Peter had said.

But he gave them special orders, not to say this to any man;

He sternly ordered and commanded them not to tell anyone,

And He strictly warned and commanded them to tell this to no one,

But he forcefully commanded ¹  them not to tell this to anyone, ² 

¹ tn The combination of the participle and verb ἐπιτιμήσας and παρήγγειλεν (epitimhsa" and parhngeilen, “commanding, he ordered”) is a hendiadys that makes the instruction emphatic.

² sn No explanation for the command not to tell this to anyone is given, but the central section of Luke, chapters 9-19, appears to reveal a reason. The disciples needed to understand who the Messiah really was and exactly what he would do before they were ready to proclaim Jesus as such. But they and the people had an expectation that needed some instruction to be correct.