The following is an excerpt from
The MacArthur New Testament Commentary on Luke 5.
After healing the man, Jesus ordered him to tell no one, for the moment. There was something the now cleansed leper needed to do at once, so the Lord commanded him, “Go and show yourself to the priest and make an offering for your cleansing, just as Moses commanded.” The process by which a cleansed leper was readmitted to society involved going to the temple for an examination by a priest, shaving, bathing, washing his clothes, offering multiple animal sacrifices, along with an offering of grain and oil (Lev. 14:1-20). The entire procedure lasted for eight days (Lev. 14:10). If he obeyed and went to recount to the priests how Jesus had healed him, it would be a powerful testimony to them that Jesus was indeed the Messiah and Son for God. This testimony would be either convincing to the priests so that they would acknowledge the claims of Christ, or if they rejected Him self-indicting, since they had personally examined the miraculously healed leper. Further, it would buy time for Jesus, since a miracle of that magnitude would surely swell the already large crowds that followed Him—crowds so huge that they had forced Him off the shore of the Sea of Galilee and into Peter’s boat.
But selfishly overjoyed at his remarkable, miraculous healing, the man ignored Jesus’ command and instead “went out and began to proclaim it freely and to spread the news around” (Mark 1:45), forfeiting the opportunity for such a powerful testimony. As a result, the news about Him was spreading even farther, and large crowds were gathering to hear Him and to be healed of their sicknesses. So vast were the crowds that Jesus “could no longer publicly enter a city, but stayed out in unpopulated areas; and they were coming to Him from everywhere” (Mark 1:45). The disobedience of the cleansed leper had put limitations on Jesus’ ministry and forced Him into the countryside away from the populated towns. The ones who could find Him in the wilderness did so, but surely many of the most disabled in the towns were not able to experience His healing word and touch.