Sin is a concept and a reality that we do not talk about enough. Our own sin, in particular, is something we tend to avoid. Why is this? The answer is that we avoid thinking and talking about our sin because we are sinful.
As I write this, I am not condemning anyone. Trust me - most of the time I feel like I (not Paul) am the chief of sinners. This is probably because when I dare to do so, I can see into the depths of my own heart much better than I can anyone else's.
One problem we may have is that we do not have an accurate definition of sin in mind. If you have time someday, take a look on-line at a variety of different church websites. Where they tell what they believe, see if they define sin. I guarantee that you will find definitions that vary a great deal.
So what is a great (and more importantly - biblical) definition of sin?
The Baptist Catechism published by Desiring God Ministries (which is patterned on the Westminster Catechism) defines sin as well as I have seen it. It reads, "Sin is transgression of the revealed will of God which teaches that we are to act in perfect holiness from a heart of faith to the glory of God."
I have never seen sin defined any better.
As a family, we use this catechism as part of our family devotional time. I am thrilled whenever I hear my three children rattle off this definition for sin. My hope is that by knowing what sin is, they will be less likely to commit it.