All right, I’ll assume that this is a genuine inquiry and not an attempt to gotcha me. I’ve had to deal with gotcha questions before.
The first question is what you mean by unrepentant sin. There are sins that we commit that we repent of, but still have a hook in us, so to speak. There are sins that a man can commit every day, and hate doing, but still has to repent of them every day.
And other times we sin without even knowing that we do. Pride. Lust. The innermost thoughts of the heart that we don’t even think about.
This is why the Christian life is a life of continual repentance until either we die or Jesus returns.
An unrepentant sinner, on the other hand, would be saying, “I know it’s a sin and I don’t care; I’m going to do it anyway. I don’t care about what the Lord says.”
A person with that kind of attitude towards the will of God either doesn’t have faith at all, or will very soon lose what faith they have. I mean, that IS what James 2 is talking about, isn’t it?
And Lutherans, at least, acknowledge that. That’s why there are instructions about excommunication (and reconciliation, for those who repent of their previously unrepentant sin) and why pastors have lots of training in church discipline.
Combined with grave matter, this is the definition of a mortal sin: sufficient reflection and full consent of the will. If ones dies without repenting of such sin then he will not enter into the kingdom of Heaven. Leaving aside the question of sacramental Confession, how does what you present as Lutheran teaching differ from Catholic?
I would also say that I appreciate that you have returned to the question. I must appreciate that it is often difficult to present the Catholic position against what are multiple Protestant ones. You should also appreciate that there are some Protestants, at least from my point of view, who seem to take an absolute view that no sin would loose them their salvation.