Look, I do not wish to debate and get into trouble. However, can I ask for clarification? First, I am not saying that I ncessarily agree with the minority view that habitual sin could cause one to lose salvation. However, neither do I necessarily disagree with it. I am undecided on the matter and have an open mind.
My position is in the middle. I don't think that sin in itself causes us to lose our status as accepted by God (i.e. justification). However habitual sin is often part of a process that leads people progressively to start ignoring God and eventually lose all faith. And at the point where someone stops seeing themselves as a follower of Christ and trusting in him, they are not justified. (Of course as someone who is Reformed, I'd say they weren't in the first place, but that's a perspective that only God has.)
Here is my question. How do we deal with the Scripture verses that clearly tell us that adulterers (and others) will NOT inherit the Kingdom of God? What if you have a Christian who is a serial adulterer? You know, there are guys like this. There are Christians who have an ongoing affiar or multiple affairs for decades. Do we really believe that these people are saved, in their present state? Is there really no end to how much we can sin and still be saved? What about a man who is a serial child sexual abuser? What about a serial rapist? It is possible that some of these men could be Christians. There certainly are many Christian men who are serial spousal abusers. Do we really believe that God will continue to forgive them, no matter how many times they physically abuse their wives?
On the one hand, Jesus and Paul both have uncompromising standards. On the other, they both emphasize God's forgiveness.
Paul gives two qualifications to the bare statements that Christians don't sin. For one, he notes that in him two things contend: the redeemed man, and a remnant of the "law of sin." (Rom 7:21 ff) Christians don't sin, but we aren't yet fully Christians. Secondly, he notes that in the end, there will be a time when the remnants of our old selves are purged, after which we truly will no longer be sinners. (i Cor 3:12 ff)
As to specific people, I don't think we can tell, which is why both Jesus and Paul tell us not to judge. Many people who sin are probably deluding themselves when they think they're followers of Christ. While justification comes from being a follower of Christ, and neither sinlessness nor any works, faith is associated with both a commitment to obey, and repentance. However we do all sin. In some cases it is the remnants of the old man, as noted by Paul. In others it is a kind of moral ignorance, which is no doubt culpable, but still real. E.g. I once had a colleague that said things about women that I would consider unacceptable. But because of his background, he didn't see it. More seriously, 150 years ago we had Christians who were brought up not to consider some people human. I think both of these categories of people had sufficient grounds that they should have know the truth, but the fact is that their abuses do not necessarily represent what they appear to be. Only God can judge whether someone is an imperfect follower or someone who claims to follow Christ but of whom Christ will at the end say he never heard of them.