All right fellow sinners, let's get right to it!
The Bible speaks of degrees of sin:
1 John 5:16-17: "If any one sees his brother committing what is not a mortal sin, he will ask, and God will give him life for those whose sin is not mortal. There is sin which is mortal; I do not say that one is to pray for that. All wrongdoing is sin, but there is sin which is not mortal."
Some translations read "deadly" instead of "mortal," but since deadly and mortal are synonymous, we're good.
Did you know that was in the Bible?* Neither did I, until just a few years ago. Since it is explicit, I don't have an explanation for why most Protestants have a problem with the concept of mortal sin. At the very least, the concept of degrees of sin is there, right? Clearly, some sins are more serious than others.
And that leads us to the actual point of this post.
The Catholic Church teaches that some sins are mortal (serious) and some are venial (less serious).
Mortal sin is what the name implies: Mortal sin = spiritual death. A mortal sin severs our friendship with God and kills the sanctifiying grace in our souls. Without sanctifying grace in our souls, we are not fit for Heaven.
Venial sin is less serious sin, which does not destroy our friendship with God. Venial sins do not kill the sanctifying grace in our souls, although they do weaken the will and darken the intellect. A million venial sins won't "add up" to a mortal sin, but a habit of venial sin does make it easier to begin to commit mortal sin.
There are three conditions that must be present before a mortal sin is committed:
1. The sin in question must be of a grave matter
2. The sin must be committed with full knowledge of its gravity
3. The sin must be committed with full consent of the will
Please note: If any of those three conditions do not apply, the person is guilty only of a venial sin. One cannot "accidentally" commit a mortal sin and fall into hell, as mortal sin requires a deliberate choice on the part of the sinner. And, if you suffer from scrupulosity, I beg you to read this post next.
The next logical question people ask is: "Where is the list of mortal sins?" The Church does not provide a definitive list, but there are helpful guidelines to aid in discernment. Some are obvious (i.e., murder; adultery) and some less so (i.e, taking advantage of the poor; extreme anger). If you suffer from scrupulosity, I would suggest you not agonize over the list of mortal sins. That's kind of like consulting Dr. Google instead of a doctor -- it's ill-advised for an anxious soul and might do more harm than good!
In summary: Mortal sin kills the life of grace, venial sin wounds the life of grace.
Remember, I call these "Little Teachings From the Bubble"! That's all I've got for today!
*We Catholics don't subscribe to the Protestant doctrine of sola scriptura (i.e., the Bible is a Christian's only authority), so it wouldn't be a deal-breaker even if it were not explicit in the Bible. More on sola scriptura in a future post.