I think sin is something which lowers our very worth. Not that we can ever gain enough points to be considered perfect by some sort of innate virtue, but I do think sin is a degrading thing.

We can desire to have more than we do. To this end, we could work hard and concientiously, we would gain reward from that. OR we could steal, covet, over-work (and thus ignore other parts of our life for material reward we don't really get to enjoy) - that would be sin.

We speak to other people. If we speak respectfully and politely, we are listened to and our company is appreciated, even desired. Or we can be rude, intolerant and loutish, which would be sin and its own punishment as fewer people wanted to be with us and our friends were not people we generally like, but will just put up with us.

Yes, doing illegal things and going against the laws of God are sins. But I think there are things that aren't covered explicitly here that are sins too, they are about our conduct and appearence (appearence of character). On contraception, I feel that if we have more children than we can support - we cannot afford to feed or clothe them properly, we resent them because we have to have them - then no contracption would be a sin. If, on the other hand, we mourn the loss of children to the extent that we become jealous or unable to cope because we use contraception then using it would be sinning. How can we properly praise God for our children if we dislike being with them?