From: Matthew 8:1-4
The Curing of a Leper
 When He (Jesus) came down from the mountain, great crowds followed Him;  and behold, a leper came to Him and knelt before Him, saying, "Lord, if You will, You can make me clean."  And He stretched out His hand and touched him, saying, "I will; be clean." And immediately his leprosy was cleansed.  And Jesus said to him, "See that you say nothing to anyone; but go, show yourself to the priest, and offer the gift that Moses commanded, for a proof to the people.
Chapters 8 and 9 of St. Matthew deal with a series of miracles worked by our Lord. The first Christians had vivid experience of the fact that the glorified Jesus was still present in His Church, confirming its teaching by signs, by miracles (Mark 16:20; Acts 14:3).
And so, St. Matthew, after giving the nucleus of Jesus' public teaching in the Sermon on the Mount (Chapters 5-7), goes on now to gather a number of miracles to support our Lord's words. Some commentators call this section--Chapters 8 and 9--"the works of the Messiah", paralleling what they called "the words of the Messiah" (the Discourse on the Mount). In Chapters 5-7 we see Jesus as the supreme lawgiver and master who teaches with divine authority, a unique authority superior to that held by Moses and the prophets. Now, in Chapters 8 and 9, He is shown as endowed with divine authority over disease, death, the elements and evil spirits. These miracles worked by Jesus Christ accredit the divine authority of His teaching.
1. The Gospel draws attention, for the third time, to the huge crowds that flocked to Jesus: literally, "many multitudes followed Him". This shows the popularity He had achieved: He was so popular that the Sanhedrin (the great council of the Jewish nation) dared not arrest Him for fear of what the people would do (cf. Matthew 21:46; 26:5; Mark 14:2). Later on, they would accuse Him before Pilate of stirring up the whole country from Judea to Galilee. And we will see Herod Antipas' eagerness to meet Jesus, of whom he has heard so much (cf. Matthew 14:1). In contrast to this huge popularity, we find the elders opposing Him and deceiving the people into calling for Jesus' execution (cf. Matthew 27:20-22).
2. The Fathers have taken the following meaning from this cure: leprosy is a vivid image of sin: it is ugly, disgusting, very contagious and difficult to cure. We are all sinners and we are all in need of God's forgiveness and grace (cf. Romans 3:23-24). The leper in the Gospel knelt down before Jesus, in all humility and trust, begging to be made clean. If we have recourse to our Savior with that kind of faith, we can be sure than He will cure the wretchedness of our souls. We should often address Christ with this short prayer, borrowed from the leper: "Lord, if You will, You can make me clean."
4. According to the Law of Moses (Leviticus 14), if a leper is cured of his disease, he should present himself to a priest, who will register the cure and give him a certificate which he needs to be reintegrated into the civil and religious life of Israel. Leviticus also prescribes the purifications and sacrifice he should offer. Jesus' instruction to the leper is, then, in keeping with the normal way of fulfilling what the laws laid down.
Source: "The Navarre Bible: Text and Commentaries". Biblical text taken from the Revised Standard Version and New Vulgate. Commentaries made by members of the Faculty of Theology of the University of Navarre, Spain. Published by Four Courts Press, Kill Lane, Blackrock, Co. Dublin, Ireland. Reprinted with permission from Four Courts Press and Scepter Publishers, the U.S. publisher.