C. S. Lewis on sinning

I found the following quote in Mere Christianity and think that it speaks very well to the issue of sin, excuse/denial of sin and its opposite -- striving for sinless perfection. It is from the chapter on sexual morality but I think it applies equally to any area:

In the first place our warped natures, the devil who tempt us, and all the contemporary propaganda for lust, combine to make us feel that the desires we are resisting are so "natural," so "healthy," and so reasonable, that it is almost perverse and abnormal to resist them....Now this, on any conceivable view, and quite apart from Christianity, must be nonsense...For any happiness, even in this world, quite a lot of restraint is going to be necessary; so the claim made by every desire, when it is strong, to be healthy and reasonable, counts for nothing. Every sane and civilised man must have some set of principles by which he chooses to reject some of his desires and permit others...

In the second place, many people are deterred from seriously attempting Christian [virtue] because they think (before trying) that it is impossible. But when a thing has to be attempted, one must never think about possibility or impossibility. Faced with an optional question in an examination paper, one considers whether one can do it or not: faced with a compulsory question, one must do the best one can. You may get some marks for a very imperfect answer: you will certainly get none for leaving the question alone...it is wonderful what you can do when you have to.

We may, indeed, be sure that perfect [virtue] -- like perfect charity -- will not be attained by any merely human efforts. You must ask for God's help. Even when you have done so, it may seem to you for a long time that no help, or less help than you need, is being given. Never mind. After each failure, ask forgiveness, pick yourself up, and try again. Very often what God first helps us toward is not the virtue itself but just this power of always trying again. For however important [any virtue] may be, this process trains us in habits of the soul which are more important still. It cures our illusions about ourselves and teaches us to depend upon God. We learn, on the one hand, that we cannot trust ourselves even in our best moments, and, on the other, that we need not despair even in our worst, for our failures are forgiven. The only fatal thing is to sit down content with anything less than perfection.

Mere Christianity, pp. 78-79

One thing I would add to this is that, so often, a choice to sin or not may be viewed from a very short perspective; i.e., the only thing in front of the person is the thing they are looking at in the here and now. Then, however, it becomes a thing to battle rather than merely a challenge to hold on to a greater vision. In other words, it becomes like Esau selling his birthright for a bowl of stew. What a price to pay! It is this short-sightedness and the resulting disarray in one's life as the far-reaching consequences of a momentary (or willful) lapse come into play that can propel one down a slope (the snowball effect, if you will) or else cause one to rationalize or otherwise deny (harden one's heart). It is such a view that may also cause one to feel oneself a naughty child before a stern and punishing God.

But if one can keep in view the true effects and cost of one's behaviors in a total picture/into-the-future kind of way, then one may also see that God is a God of the long haul and One not so concerned with sin-scorecards as with the (eternal) well-being of ourselves and those we affect.