Struggling with the dialectic of faith and works

This morning my son and I read the second Faith chapter in C.S. Lewis, Mere Christianity. He considers our struggle to understand the relative role of faith in Christ and our own efforts in living as a Christian. I found the following passages particularly helpful:

Christians have often disputed as to whether what leads the Christian home is good actions, or Faith in Christ. I have no right really to speak on such a difficult question, but it does seem to me like asking which blade in a pair of scissors is most necessary. A serious moral effort is the only thing that will bring you to the point where you throw up the sponge. Faith in Christ is the only thing to save you from despair at that point: and out of that Faith in Him good actions must inevitably come....

The Bible really seems to clinch the matter when it puts. the two things together into one amazing sentence. The first half is, 'Work out your own salvation with fear and trembling'- which looks as if everything depended on us and our good actions: but the second half goes on, 'For it is God who worketh in you'- which looks as if God did everything and we nothing. I am afraid that is the sort of thing we come up against in Christianity. I am puzzled, but I am not surprised. You see, we are now trying to understand, and to separate into watertight compartments, what exactly God does and what man does when God and man are working together. And, of course, we begin by thinking it is like two men working together, so that you could say, 'He did this bit and I did that.' But this way of thinking breaks down. God is not like that. He is inside you as well as outside: even if we could understand who did what, I do not think human language could properly express it. In the attempt to express it different Churches say different things. But you will find that even those who insist most strongly on the importance of good actions tell you need Faith; and even those who insist most strongly on Faith tell you to do good actions. At any rate that is as far as I can go.

The Bible verse Lewis is quoting is Phillipians 2:11-13. Until now I had not appreciated the logical tension (or dialectic) inherent in that verse.