There is an impulse in the fallen human heart—all our hearts—to forget that gratitude is a spontaneous response of joy to receiving something over and above what we paid for. When we forget this, what happens is that gratitude starts to be misused and distorted as an impulse to pay for the very thing that came to us “gratis.” This terrible moment is the birthplace of the “debtor’s ethic.” The debtor’s ethic says, “Because you have done something good for me, I feel indebted to do something good for you.” This impulse is not what gratitude was designed to produce. God meant gratitude to be a spontaneous expression of pleasure in the gift and the good will of another. He did not mean it to be an impulse to return favors. If gratitude is twisted into a sense of debt, it gives birth to the debtor’s ethic—and the effect is to nullify grace.
~John Piper, Future Grace, p. 32
Here is the legalistic twist which can happen to gratitude. When grace if offered to us we slyly try to pay it back by doing works of “gratitude.” We see the grace offered to us through the work of Christ, receive it, but then immediately move pay it back. The legalistic habit starts living again. But the habit hides itself under a cloak of “holy gratitude.” We begin telling ourselves that we have to work so much harder in doing good works because Christ gave us so much. Christ’s death becomes a legalistic law which we place ourselves under. The very reversal to what Christ’s death was meant to be!
“but whoever drinks of the water that I will give him will never be thirsty again. The water that I will give him will become in him a spring of water welling up to eternal life.” (John 4:14)