Based on his reading of Karl Barth's commentary on Romans, Robert E. Willis writes the following:
"Sanctification, then, is real. It is obedience that poses a continuing problem. . . . Are we really obedient? Do we really let the divine disturbance fall upon us, so that our lives are opened for service in love to God and our neighbor? There is no way of answering these questions directly. . . . Man lacks the capacity to tell himself that he is obedient, that his actions are performed in response to the command of God. The only possibility ... [is to act, and to] leave the results, the assessing of those actions, entirely in the hands of God. . . .
[Thus:] If the issue of obedience is not to be decided by direct reference to specific actions and possibilities, then we are forewarned against any attempt to set up orders and structures within history to which the adjective 'Christian' could automatically be attached. This occurs whenever we attempt to speak unambiguously of a 'Christian' world-view, morality, or art; or of a 'Christian' personality, family, party, or newspaper. These serve merely to mark human efforts to establish continuity between the actions of man and the prerogative of God; or rather, they involve a continual ignoring of that prerogative. Barth's treatment of obedience is thus designed, in the first instance, to safeguard the freedom of God."
This of course raises questions about, among other things, Christian ethics and assurance of faith.
In the case of the latter: Can we discern whether we are 'Christians'? Can we have assurance of faith? I think the answer is in the question. Our salvation is a matter of faith. Either Jesus raised from the dead or he didn't. Our salvation rises and falls with that. Am I a Christian? I have no way of proving it. I believe it to be so because I believe Jesus Christ has reconciled all to God.
In the case of the former: Can we speak of what it means to act 'Christianly'? I think later on in his career Barth gets more clear about this, indicating that there are certain frames of reference within which decidedly Christian activity takes place and there is in the Christian community the belief that by invocation of God and hearing of His command in the present there can be confident obedience along certain lines. But even then the confidence is not in oneself but in the grace of God to take any attempt at obedience and sanctify it and make it good.
This is the kind of stuff I've been thinking about for what seems like months on end now. I'd be interested to hear whether it is at all intelligible and, if so, whether it seems to be on to something or not.
(quotations from Robert E. Willis, The Ethics of Karl Barth, p. 56-57)