Karl Barth, More on Gratitude
The being of man is a being in gratitude. His history as constituted by the Word of the grace of God, his being therefore, continues and must continue in the fact that it is a being in gratitude. Merely as the promise of the grace of God, it could not continue, or be the history of man, his own being. The promise is, like its content, the affair of God and not of man. As it cannot be gracious to itself, it cannot tell itself that God is gracious to it. This it can only hear. The Word of grace and therefore grace itself, it can only receive. But as it does this, as it is content to be what it is by this Word, as it thus exists by its openness towards God, the question is decided that it is a being in gratitude. It has not taken the grace of God but the latter has come to it; it has not opened itself but God has opened it and made it this open being. And it now is what it has been made. But it cannot be without itself actualising this event. It is, as it is under an obligation to the God who has seized the initiative in starting this history. . . .
The grace of God demands that it should be accepted as such. It calls for gratitude. The fact that it finds gratitude, that the God who is gracious to His creature is honoured in the world of creation, is the being of man, and this being engaged in its characteristic activity. Hidden in thanksgiving, and therefore in the act of man, grace itself, which came from God in His Word, now returns to God, to its source of origin. Gratitude, the acceptance of grace, can itself be understood only as grace. Man does nothing special, nothing peculiar or arbitrary, when he thanks God. He is permitted to thank God. He has freedom to do so. And yet it is true that the form of grace in this return to it original source is man's action and deed, the being of man as subject.
Karl Barth, Church Dogmatics, edited by G. W. Bromiley and T. F. Torrance, III/2 (Edinburgh: T. & T. Clark, 1960), pp. 167-168, emphasis added.