Along with our failure to honor God, Romans 1:21 says our lack of gratitude to Him is the other primal sin that motivates all of the various forms of wickedness that are on display in human conduct. Like the error we commit in dishonoring God, it is also easy to see how ingratitude motivates a host of other evils. For instance, if we are not grateful to God for all of the blessings that He has given us, we will quickly begin to feel as if we have been cheated somehow. This will blossom into covetousness as we envy others whom we perceive to be more blessed than we are, and we might even go further into theft or adultery, wherein we take things that are not rightfully ours.
Biblical ethics have gratitude at their core, for it is always thankfulness to the Lord that is to motivate our obedience. This is evident from the structures of the biblical narrative itself. When God speaks to His people after the fall, He always reminds us of how much He has done for them before He delivers His laws. The Ten Commandments were not given to the ancient Israelites until after the Lord rescued them from slavery in Egypt (Ex. 20:1–17). In their epistles, Peter, Paul, and the other apostles generally lay out the great truths of redemption before they make application of those truths in practical, ethical matters. From first to last, thankfulness is one of the major animating impulses of a true Christian ethic.
According to the Word of God, gratitude is not simply something that we feel but something that we must demonstrate to others. When interpreters look at the account of the cleansing of the ten lepers in Luke 17:11–19, they often draw the distinction between one leper who was thankful and nine who were ungrateful. Yet this is not exactly what we see in the passage. We have no reason to believe that the nine who did not immediately thank Jesus for their healing felt no gratitude, for who among us would not be tempted to run home immediately and share the good news if we should be healed of some terrible ailment? This can be done even as we are feeling thankful in our hearts toward the healer. No, the real difference between the one who went back to Jesus and the nine who did not is that the one who returned displayed His gratitude while the others kept it to themselves. Christian thankfulness will always display itself in good deeds and verbal expressions of gratitude.