Jesus had a special word for a leper (one of ten and a Samaritan, not a Jew) who returned to give praise and thanks for his healing while the others (also healed) went on their way (Luke 17). Were they grateful? Surely, but was the complete healing, ‘Your faith has made you well (whole)’, the experience of the one alone, and was thanks the seal and sign of healing faith even more so than physical restoration? C.S.Lewis commented on the completion that gratitude gives to any blessing in a letter to his brother in January 1940.
‘It seems almost brutal to describe a January walk taken without you in a letter to you, but I suppose ‘concealment is in vain’. . . . I dined at the Harwoods that night and came away, on Tuesday morning, as you said in your last letter ‘thanking the Giver’ which, by the way, is the completion of a pleasure. One of the things about being an unbeliever is that the steam or ‘spirit’ (in the chemical sense) given off by experiences has nowhere to go to.
From The Collected Letters of C.S.Lewis, Volume II
sermons and soda water 