I’ve just finished writing an essay outlining the shape of Karl Barth’s ethic, key to which is the concept of Divine Command. To prevent his account sounding like a divine tyrant or a voluntaristic thunderstrike like other Divine Command Theories, he provides the following great quote from CD II/2, p 587:
It is true, of course, that this command also says: Do this and do not do that. But in the mouth of God this means something different. Do this—not because an outer or inner voice now requires this of you, not because it must be so in virtue of any necessity rooted in the nature and structure of the cosmos or of man, but: Do this, because in so doing you make it true that your rejection has been rejected in the death of Jesus on the cross, that for His sake your sin has been forgiven. Do this, because in Jesus Christ you have been born anew in the image of God. Do it in the freedom to which you have been chosen and called, because in this freedom you may do this, and can do only this. For this, and not for any other reason, do this. You may do it. And: Do not do this—not because you hear an inner or outer voice which seeks to make it doubtful or dreadful for you, not because there is any power in heaven or on earth to prevent or spoil or for some reason forbid it. No, but: Do not do this, because it would be a continuation of the fall of Adam, because it would not correspond to the grace addressed to you but contradict it, because you would have to do it as the captive which you certainly are not, because you, the free person, are exempted from the necessity of doing it—really exempted by the fact that you have been made righteous and glorious in the resurrection of Jesus Christ, that you have actually been cut off by Him from this very possibility. This is how the command of God speaks.