"If you see your brother or sister committing what is not a mortal sin, you will ask,and God will give life to such a one--to those whose sin is not mortal. There is sin that is mortal; I do not say that you should pray about that. All wrondgoing is sin, but there is sin that is not mortal. We know that those who are born of God do not sin, but the one who was born of God protects them, and the evil one does not touch them." I John 5:16-18
If I am understanding this and MH correctly. . .
for the believer, there is sin that does not lead to death. Furthermore, he is protected and prohibited from that sin that does lead to death. Impenitence and unbelief lead to death, but "the gospel does not positively and peremptorily threaten death to the more visible sins of the members of Christ but only some gospel-chastisement" (MH 1 John 5:14-17). A comfort and solution to the "What if I die before asking forgiveness for a particular act?" question.
For those sins we do commit, which are not mortal, we may not only ask forgiveness for ourselves, but also for believing brothers with expectation of forgiveness. What grace that not only protects me from mortal sin, but also exchanges my non-mortal sin for life when a friend recognizes my need, albeit my own ignorance or inattention.