I think this quote relates to some of the ideas I presented in my last post, and Ellul says it so much more eloquently than I can:
"Henceforth we must give up the idea that we can decrease our sin by our virtues. We must give up believing that we can 'improve' the world, that at least we can make man better, even if we cannot make him happy. At the same time, if we take this situation of the Christian seriously, we must refuse to further the disintegrating tendency in the world. We must not say to ourselves, 'We can't do anything about it!'
Thus we seem caught between two necessities, which nothing can alter: on the one hand it is impossible for us to make this world less sinful; on the other hand it is impossible for us to accept it as it is. If we refuse either the one or the other, we are actually not accepting the situation in which God has placed us... just as we are involved in the tension of sin and grace, so also we are involved in the tension between these two contradictory demands. It is a very painful, and a very uncomfortable, situation, but it is the only position which can be fruitful for the action of the Christian in the world... we must accept this tension and live in it."