[That] which we maintain when we describe the covenant as the covenant of grace is that the covenant engages man as the partner of God only, but actually and necessarily, to gratitude. On the side of God it is only a matter of free grace and this in the form of benefit. For the other partner in the covenant to whom God turns in this grace, the only proper thing, but the thing which is unconditionally and inescapably demanded, is that he should be thankful. How can anything more or different be asked of man? The only answer to [grace] is [gratitude]. But how can it be doubted for a moment that this is in fact asked of him?
[Grace] always demands the answer of [gratitude]. Grace and gratitude belong together like heaven and earth. Grace evokes gratitude like the voice an echo. Gratitude follows grace like thunder lightning. Not by virtue of any necessity of the concepts as such. But we are speaking of the grace of the God who is God for man, and of the gratitude of man as his response to this grace. Here, at any rate, the two belong together, so that only gratitude can correspond to grace, and this correspondence cannot fail. Its failure, ingratitude, is sin, transgression. Radically and basically all sin is simply ingratitude—man’s refusal of the one but necessary thing which is proper to and is required of him with whom God has graciously entered into covenant. As far as man is concerned there can be no question of anything but gratitude; but gratitude is the complement which man must necessarily fulfil. [Barth, K., 2004. Church dogmatics, IV/1. London; New York: T&T Clark. pp.41-42].