Today's Gospel is the story of the ten lepers who were healed by Jesus. When only one came back in thanks, Jesus seemed put out. "Where are the other nine?" Jesus wanted to have that "one on one" time with each one, to confirm the healing and remind each of them, "It is your faith that has saved you." (In Greek, "heal" and "save" are the same word.)
Even the verse before the Gospel (the Alleluia verse) says that it is God's will that we should give thanks to God. In other words, thanksgiving is our human vocation.