Sin is like a red rubber ball that gains too much momentum & ends up being launched out into the road. Its manageable in the yard, but once it crosses that boundary, the potential for harm increases, not only for the child, but for those out on the street as well. The sin is in the momentum. The sin is in the pursuit. Some sin is accidental, such as a ball going over a fence. Some sin is deliberate, as in a... ball... going... over a fence? What motivated the ball? Well, the child, of course. Did the child know the potential danger? Did he/she mean to keep it behind the fence & failed? Was the ball deliberately launched? As for pursuit, did the child seek adult intervention or did he/she go vaulting off into the street, risking life & limb?
In Catholic belief, there are two types of sin: venial & mortal. Venial sins comprise of those "oopses" & tend to be accidental. We simply need to go to God & ask forgiveness & help. Its my understanding that venial sins don't lead to death. But the Bible says there is a sin (plural?) that DOES. Catholics believe this falls under the category of mortal sin, which must meet three conditions to qualify: It is a grave matter (premeditated), there is full knowledge the deed is sin & there is full consent to do it despite.
In this case, mortal sin must be confessed not only to God, but also to a priest who will administer the sacrament of reconciliation. Without this sacrament, one is said to be in danger of dying outside of God's grace with a one way ticket to hell. Sounds harsh. Why would one need a priest for anything if Jesus paid the price for all our sins? Why not just confess to God & be done? I believe the priest in this instance is something like a paramedic. Perhaps we've gone out after our ball & we got hit. Reconciliation is God's way of probing us & exposing our wounds so we can be restored. Sometimes treatment is quick & easy. Sometimes we need a ride in the ambulance & a hospital stay. Either way, I'm of the mind that this is actually what Jesus paid for. We still endure the consequence of sin, but help is there when we need it.
So what's so great about sin? It reveals whether my faith goes beyond words or not. It is an agent that humbles me one way or another, but always provides an opportunity for grace. In the case of venial sin, it is a chance for learning the basics of how to be human. Concerning mortal sin, it is a wake up call that reveals the weight of God's gift of life.