What the Bible says
“See thou say nothing to any man: but go thy way, shew thyself to the priest, and offer for thy cleansing those things which Moses commanded, for a testimony unto them.”
Mark 1:44 (KJV)
“But he went out, and began to publish it much, and to blaze abroad the matter, insomuch that Jesus could no more openly enter into the city, but was without in desert places.”
Mark 1:45 (KJV)
“He charged them that they should tell no man what things they had seen, till the Son of man were risen from the dead.”
Mark 9:9 (KJV)
What happened when people didn't listen
After Jesus healed a leper and told him to say nothing, the man told everyone. Mark records the result: Jesus could no longer openly enter a city. The crowds that came for wonders made it harder for him to preach, which he said was why he had come (Mark 1:38).
The wrong kind of king
Many hoped the Messiah would overthrow Rome. After he fed the five thousand, the people wanted to take him by force and make him king (John 6:15). Jesus kept his identity quiet until he could show what kind of King he was — one who would wear a crown of thorns.
Until he is risen
Coming down from the mountain of the transfiguration, Jesus told the disciples to tell no one until he had risen from the dead. The silence had an end date. After the resurrection he sent them to all nations. And where there was no danger of a crowd, as with the man freed from Legion, he said the opposite: go home and tell them (Mark 5:19).
Common questions
What is the 'messianic secret'?
The name scholars give to Jesus's repeated instructions in Mark to keep his identity and miracles quiet until the right time.
Did Jesus ever tell someone to spread the news?
Yes. He told the man freed from Legion, Go home to thy friends, and tell them how great things the Lord hath done for thee (Mark 5:19).