In "Biblical Perspective", Dr. Gayle Woods writes:

Were there not ten cleansed? but where are the nine? Do we hear a note of disappointment in the words of Jesus? Is there an indication that He seemed to be somewhat puzzled by the fact that nine of the ten men who had been healed did not seem to place great value on what He had done for them?
This account should be a serious reminder to the people of God that we must be careful not to become familiar with the work of God to the point that we lose the sense of wonder and amazement. When the awesomeness of His glory begins to dim, we need to fall on our faces at His feet once again to renew our commitment of love to the one who made the difference in our lives.

Discussion: List possible reasons why the nine lepers failed to show gratitude to God.
Discussion: What are ways we today become too familiar that we fail to worship?
Source: Miracles of Jesus: Adult Teacher's Insights, page 31.