Jesus said in reply, "Ten were cleansed, were they not? Where are the other nine? Has none but this foreigner returned to give thanks to God?"
Gospel's Commentary
Today, Jesus Christ has healed 10 lepers, but only 1 has come to thank him. Unbelievable! Jesus has done them the greatest favor of their lives, because leprosy was an incurable disease and lepers were socially marginalized ... Only one worshiped God by thanking Him for the miracle!
—The human being is the only “animal” (living being) capable of recognizing how much we owe to God and, consequently, thanking Him. And yet, how easily we forget! Camels or crocodiles don't give thanks to God either ...