William Burkitt on Luke 17:17

In the face of these ten lepers we may, as in a glass, behold the face and complexion of all mankind. How few are there, oh Lord! Scarce more than one in ten, who after single mercies return suitable thanks. Men howl to God upon their beds, but run away from God as soon as they are raised up by him.

Observe farther, what an exact account Christ keeps of his own dispensed favors: Were there not ten cleansed? He forgets our sins, but records his own mercies. It is one of his glorious titles, a God forgiving and forgetting iniquity; but his mercies are over all his works, and deserve everlasting remembrance. God keeps a register of his mercies towards us. Oh shall we not record the favors received from him, at once declare his bounty towards us, and our thankfulness towards him?

Observe lastly, the thankful leper was a Samaritan, but the nine that were unthankful were Israelites.

Learn thence, that the more we are bound to God, the more shameful is our ingratitude towards him; where God may justly expect the greatest returns of praise and service, he sometimes receives least. God has more rent, and better paid him, from a smokey cottage, than he has from some stately palaces.