This may seem a quite basic question, and you may think this particular pastor has spent a bit too much time in his office. Doesn't everybody, even non-Christians, have a pretty solid idea what sin is? I mean, a whole lot could list at least 4 of the 10 commandments, and that would get you started at least, wouldn't it? That's true, but the question I'm asking is less "What kinds of things are sin?" and more "What makes sin sinful?"
A lot of people, including a lot of Christians, think of sin as being roughly equivalent to "breaking a rule." That is, life is something like a baseball game with God as Cosmic Umpire. Everybody knows the rules, knows that there are penalties for breaking them and, if they believe the Bible, understands the penalties for rule-breaking are ultimately severe. But there is a great sense that God's "rules," like the rules of baseball, are finally arbitrary, rooted in not much other than God's personal preferences. For example: There is no particular reason why a base runner should have to "tag up," why the strike zone should be where it is, why the distance between bases is precisely 90 feet and not, say, 150 feet, why there are three outs per team, per inning, or 9 innings in a standard game. The reasons are located in the essentially arbritrary decisions of Mr. Doubleday back when, added to 150 plus years of baseball tradition since. Likewise, many people think, there is no good reason beyond God's personal preferences why non-marital sex in all its forms, drunkenness, coarse talk, pride, taking what isn't yours instead of working, rage, "and things like these" are all sinful instead of acceptable.
But such thoughts are off base in more ways than one. First, and most subtly, it is the very influence of sin upon us that leads us to think that God's moral laws are abritarily, rather than transcendantly, founded. We think "Well, I know I shouldn't, but since 'nobody's perfect,' isn't all this wrath and judgment business over my little indiscretions really all a bit much? Why is God so worked up about things?" But God's moral laws are not, in the final analysis, arbitrary. They are rooted in His character, in the kind of being He is and in the manner in which He as the Triune God exists and relates between the Persons. His moral law is based not on arbritary decisions: e.g., "I think I'll declare non-marital sex sinful instead of holy." Instead it is based on the facts of God's own character; the way that He behaves and the kind of being He is requires those specific commands be given to creatures who, after all, are made in His image to be like Him and partake of His nature (2 Peter 1:3-4).
Moreover, because sin is not simply the breaking of some arbritary rule, we need to see it for what it is: An attempt to declare revolution, dethroning God and putting us in His place. When we sin what we are saying is that we are sufficient bases to determine the true, the right, and the good, that our character exceeds that of God, and that we, rather than God should ultimately be followed and obeyed. It is, in all of its varieties an attempt (to borrow a phrase from D. A. Carson) to "de-God God." It's not just rule-breaking; it's rebellion, treason, sedition, a miniature revolt against our Creator in whose image we are made. Thus when we sin we aren't simply choosing to do other than God would want; we are setting ourselves up as God and telling the real one to shuffle off. That act of traitorous war-making on God, which we repeat every. single. time that we sin is really sinful and why its just penalty is death.