Matthew 16:20 - Ellicott's Commentary On The Whole Bible

Then charged he his disciples that they should tell no man. — We may venture to analyse what we may reverently call the motives of this reticence. Had the disciples gone about, not only as proclaiming the kingdom and as preachers of repentance, but sounding the watchword that the Christ had come, it might not have been difficult for them to gather round Him the homage of excited crowds. It was not such homage, however, that He sought, but that which had its root in a deeper faith. It tended to present a false aspect of His kingdom to the minds of men; it tended also to prevent the consummation to which He was now directing the thoughts of His disciples as the necessary condition of His entering on the glory of His kingdom. The zeal of the multitude to make him a king after their own fashion (John 6:15) was what He deprecated and shunned.