What does Mark 1:43 mean?

On a single day in Capernaum, Jesus freed a demon-possessed man and healed Simon Peter's mother-in-law, who was suffering from a serious fever. Within hours, the people of Capernaum came in such numbers that Jesus felt the need to take His disciples and go to another town. His primary mission is to teach, not perform miracles, but even in His travels a man with leprosy finds Him and asks to be made clean.

Jesus obliges but, perhaps thinking of the crowds in Capernaum, tells the man, go away, don't stay in the area or spread the news about the miracle. Jesus is there to teach, first and foremost, but the news of His ability to miraculously heal is already making this ministry difficult. He wants to teach in synagogues: relatively quiet places. There, His claims about fulfilling the Old Testament and being the Jewish Messiah can be contemplated and understood in a legitimate setting. That would be impossible if the crowds that followed Him were so big He couldn't go into a town. And while Jesus is more than willing to teach a large group of people, that would be difficult if He were swarming with people wanting to be healed. So He asks the man to leave, go to the priests, and have his healing officially validated.

It's very difficult to determine when this healing happened, since the Gospel accounts are not always in chronological order. Ancient texts such as the Gospels are frequently written in a topical order. Matthew 8:1–4 tells the story of a similar healing which occurred after the Sermon on the Mount. In that case, the healing took place amidst a great crowd. Luke 5:12–16 matches Mark's chronology better, but not perfectly, and gives an almost identical reading.