From: Luke 17:11-19
The Ten Lepers
 On the way to Jerusalem He (Jesus) was passing along between Samaria and Galilee.  And as He entered the village, He was met by ten lepers, who stood at a distance  and lifted up their voices and said, "Jesus, Master, have mercy on us."  When He saw them He said to them, "Go and show yourselves to the priests." And as they went they were cleansed.  Then one of them, when he saw that he was healed, turned back, praising God with a loud voice;  and he fell on his face at Jesus' feet, giving Him thanks. Now he was a Samaritan.  Then said Jesus, "Were not ten cleansed? Where are the nine?  Was no one found to return and give praise to God except this foreigner?"  And He said to him, "Rise and go your way; your faith has made you well."
11-19. The setting of this episode explains how a Samaritan could be in the company of Jews. There was no love lost between Jews and Samaritans (cf. John 4:9), but shared pain, in the case of these lepers, overcame racial antipathy.
The Law of Moses laid down, to prevent the spread of the disease, that lepers should live away from other people and should let it be known that they were suffering from this disease (cf. Leviticus 13:45-46). This explains why they did not come right up to Jesus and His group, but instead begged His help by shouting from a distance.
Before curing them our Lord orders them to go to the priests to have their cure certified (cf. Leviticus 14:2ff), and to perform the rites laid down. The lepers' obedience is a sign of faith in Jesus' words. And, in fact, soon after setting out they are cleansed.
However, only one of them, the Samaritan, who returns praising God and showing his gratitude for the miracle, is given a much greater gift than the cure of leprosy. Jesus says as much: "Your faith has made you well" (verse 19) and praises the man's gratefulness. The Gospel records this event to teach us the value of gratefulness: "Get used to lifting your heart to God, in acts of thanksgiving, many times a day.
Because He gives you this and that. Because you have been despised. Because you haven't what you need or because you have.
"Because He made His Mother so beautiful, His Mother who is also your Mother. Because He created the sun and the moon and this animal and that plant. Because He made that man eloquent and you He left tongue-tied....
"Thank Him for everything, because everything is good" ([St] J. Escriva, "The Way", 268).
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.