One of them, when he saw that he was healed, returned with a loud voice glorifying God, and fell down on his face at His feet, giving Him thanks. And he was a Samaritan. Jesus said, “Were not the ten cleansed? Where are the nine?”
— Luke 17:15-17
This passage shows something of the nature of ingratitude. It is an astonishment to God that His beneficences do not, indeed, call forth expressions of gratitude. Ingratitude is a very serious sin.
This is certainly brought out in the first chapter of Romans, where Paul describes the sinfulness of the heathen world and catalogs a great list of sins. Read the last half of the first chapter of Romans and you will see how the heathen world had sunk deeper and deeper into the vilest forms of depravity. Finally, when you trace it all back, what do you find? “[A]lthough they knew God, they did not glorify Him or give thanks to Him as God … Therefore God gave them up to dishonorable passions” (Romans 1:21, 26).
Ingratitude and thanklessness are wellsprings out of which flowed eventually all of these other sins. The person who commits all these sins mentioned in Romans 1 is a person who is not grateful. You cannot be praising God and thanking God for what He has done for you while engaging in the type of activities described this chapter.