Wolf Krotke on Barth's Doctrine of Sin
If the 'good nature' of human beings is not a condition in and of itself, it certainly only exists at all insofar as it is lived out by men and women. Persons who do not live out their being are not human persons; they have no being. Hence, if humans are only human insofar as they live out their good nature, and if they live out their good nature only as those who sin, then they only possess their good nature as a perverted, totally corrupted nature. Accordingly, Barth can only think of the corruption of human being or nature as the 'event of their corruption.' No sphere of human existence is exempted from the event of this corrupting. The human creature is 'godless precisely in the good as good...and has fallen prey to nothingness precisely in his essentiality.'
In sum: the being of the human creature qua sinner remains ontologically constituted by the grace of God. Humans constitute their being as sinners by sinning. Several things follow from this. First, there is no perennially good 'relic or core of goodness which persists in man and in spite of his sin'; the being of sinners does not relate to human being as one quantum to another. Humans remain totally human and are totally sinners. Second, there is no 'time in which man is not a transgressor.' And third, there are 'in the whole sphere of human activities...no exceptions to the sin and corruption of man,' for under God's grace there are 'no spheres which are neutral, but only spheres of decision,' and humans have chosen in favor of sin.
The momentousness of human guilt is reflected in the enacted existence of their being: sinful humans can no longer turn to God of their own accord and by their own power. indeed, through the misuse of freedom, the liberum arbitrium given humans by God becomes a servum arbitrium.