I just ate a muffin. A blue-berry muffin. A blue-berry muffin with cinnamon glaze. A four-day-old blueberry muffin with cinnamon glaze. And it was moldy! I don't notice at first, though. In fact, I was nearly done eating it when, to my shock and dismay, I discovered the mold, blithely covering the piece of muffin on my fork, only inches away from my mouth.
In a fit of repulsion, I haplessly spit out the piece that was still in my mouth, rushed to the bathroom, and proceeded to irrigate my mouth with large amounts of water. What if I got sick? Would I need to pump my stomach? Or would the anti-mildew bathroom cleaner do the trick, if I swirled it around a little bit?
There's a lesson in this, of course. Nothing happens by accident, right?
I think sin is like eating a moldy muffin. After all, there's always something good about sin, just like there was about the muffin. If there weren't, why would we do it in the first place? But there's something bad mixed in with the good, and that's where the sin resides. Muffins are well and good, and it's a reasonable thing to eat them now and then. But moldy muffins--herein lies the disorder. The reasonableness of eating the muffin was transformed into unreasonableness because the muffin was moldy. Why is it unreasonable? Because eating a moldy muffin is bad for your health! At least, it can't be good for you, even if it doesn't do much permanent harm. One could say, then, that it is wrong to eat a moldy muffin precisely because it is bad for you. Hence the converse is not true. That is, it's bad for you not because it is wrong--as if it were simply the breaking of some arbitrary rule--but because it is unreasonable and harmful.
This is how I see sin, then. The ten commandments, for example, aren't just arbitrary rules; rather, they correspond to our human nature and to what comprises healthy relationships--with God and with other people. If I steal, for example, it is like eating the moldy muffin. There's something good about stealing, after all: the actual thing which I acquire by stealing! But the bad which is mixed in with this good is like the mold on the muffin: the thing which I acquire belongs to someone else, and he or she hasn't given me permission to take it! This introduces disorder into the relationship, as well as disorder into the heart of the person who steals. Ultimately, then, it is harmful.
And just like I instinctively wanted to wash out my mouth after I ate the moldy muffin, sin makes us feel the need to repair the damage we've done. This feeling is usually felt as "guilt"--but unless the guilt is followed by some real action that repairs the damage, the guilt is useless. One needs to recognize how the action is disordered, how it harms oneself and one's relationships, and then decide to try to avoid that action in the future. This is what I would call conversion of heart. I've certainly learned my lesson about eating moldy muffins, and I'm whole-heartedly converting to eating fresh, non-moldy muffins from now on! And I'm going to try to avoid the same mistake in the future: look before you bite!
My dad ate one and he isn't sick!
The analogy still holds, though. What if he had eaten ten moldy muffins? Do you think he would have gotten sick?
There are different types of sin because the human person is complex, and there are different ways of acting contrary to what is good for us.
For example, a little alcohol is harmless and probably even good for you. But if taken to excess, to the point of drunkenness, then one has begun to act unreasonably, against human nature.
A different type of sin is murder. If you do it even just once, it is harmful--not just to the person murdered, of course, but to the murderer, as well.
The first type of sin, dealing with alcohol, is an action against the virtue of temperance. As such, there is leeway between two extremes: either too much alcohol, or too little (what that actually means could be interpreted in different ways, I suppose). But the sin of murder is an action against the virtue of justice, and, in this case, against the dignity of the human person. There's no room for leeway--it is an example of a moral absolute.
With that said, I want to add: I'm glad that your Dad didn't get sick!