The verse in question reads, "If any one sees his brother committing what is not a mortal sin, he will ask, and he 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" (1 John 5.16). A literal translation of the passage reads, a "sin unto death"thus, a mortal sin. So, what is John writing about?
The Bible clearly delineates between sins. Some sins are seen as worse than others; however, more often than not it is the motivation and knowledge behind a sin that makes it more serious. In Exodus 34.7 the three primary Hebrew words for sin are listed. These words are typically translated sin, transgression, and iniquity. According to a classical understanding of these words, a sin is missing the mark. You were going in the right direction, but you veered or fell short. A transgression is going astray. You had good intentions, but you took the wrong path. Iniquity is much more serious. An iniquity is when you knew better, but you intentionally chose to do wrongeven knowing the consequences. New Testament Greek has a similar construct of these words.
But what is a mortal sin? As I studied the passage in question I was struck at how little information my Protestant scholars provided on the subject. Indeed, in one commentary on the subject the scholar wrote, ". . . mortal sinwhatever that is." Others cautiously suggest the only mortal sin is to not accept Christ as Savior. The only problem with this notion is 1st John 5.16 seems to indicate one can be seen committing such a sinand not accepting Christ as Savior is a sin of omissionsomething you don't do. So, to try and understand what a mortal sin is, we turn to the oldest church in the worldthe Roman Catholic Church.
The Catholic Church asserts there are two kinds of sin: venial and mortal. A mortal sin is one that causes damnation, while a venial sin does not. The list of mortal sins, according to the Catholic Church, mostly has to do with church law. But for any sin to be mortal it must meet three criteria: (1) It must be a serious matter. This means the sin must be completely out of line with the commandments to love and honor God. (2) The transgressor must have sufficient reflection. This means one has to have the knowledge that the sin is out of line with God's commands and chooses to do it anyway. (3) There must be full consent of the will. This means the person about to commit a sinful act knows s/he's about to commit a mortal sin and opts to commit it anyway. With this definition in hand, it seems what the Catholic Church calls a mortal sin is similar to what scripture calls "iniquity"a willful, informed transgression of the commandments of God.
Can a mortal sin be forgiven? Theologians differ, but Christ asserted that the only unforgivable sin is blasphemy of the Spirit of God (Matthew 12.31). However, John clearly has reservations about those who have deliberately committed a mortal sin. "There is sin which is mortal; I do not say that one is to pray for that" (1 John 5.16b)in other words, you can pray for forgiveness for a mortal sin, but. . . .
As we've seen, mortal sins are those committed with willful and informed intent. When someone knows full well that what they're about to do (or choosing not to do) is wrong and doesn't care, then provisions for forgiveness may be rather scarce. Maybe not, but one needs to consider the risk. So, a word for the wiseDon't.