Sorry for the delay; I was out sick most of yesterday.
Btw, roofus, it isn’t necessary to requote everything from my original post (especially when it’s just the previous post {g}) in order to add a comment to it.
You and Bob 1 (or would he be Bob 2?? 
) are having a fine discussion that I’m loath to interrupt. But you did ask me a question or two on how I read and reconcile certain portions of Paul’s behavior in the epistles, including in reference back to Jesus. So…
That depends on what you mean by ‘outside of grace’. I wouldn’t be much of a universalist, after all, if I thought there were any sins that God would not seek to save the sinner from. 
I strongly agree with George MacDonald, that the only unforgiveable sin is the one we refuse to come out of. It doesn’t matter what that sin specifically is: so long as we refuse to repent of it (which can only be done with God’s help, though we don’t necessarily have to be conscious it’s being done with God’s help), we cannot be forgiven. That doesn’t mean God will ever give up acting toward leading us to renounce that sin and be cleaned (or so I find and believe); but the reconciliation of fair-togetherness between God and man does require the man, as a person, to renounce his sins and choose to cooperate with God. God graciously accepts even a little of this: the rebel on the cross being perhaps the best example in all scripture of this principle. For no one can give even two-bits of charity without renouncing sin in his life somewhere. Even those who give a cup of water for the sake of saving someone else, will not lose their reward.
But: though God is longsuffering over us, sooner or later (or even sooner and later!) a time eventually comes when God decides we have to be punished. I don’t know that there is one particular go-to sin more heinous than another, that automatically results in this. Any sin would do; it’s the attitude of the heart that God is paying attention to, though. (Which is why merely ‘doing good works’, or merely doing anything else, cannot ever be enough to ‘earn’ our salvation from sin.)
In regard to the man being cast from the community in 1 Cor 5: the larger contexts of the epistle indicate that he was a chief of the factionlizers, too! (Including probably the main guy Paul is aiming at in the famous 15th chapter, concerning those who are teaching there is no Resurrection.) One key distinction seems to be that Stepmom-Sleeping Guy (as I like to call him) was an Epicuian factionalizer, rather than someone factionalizing within the Judeo-Christian group. It’s important to keep in mind, that in the Greco-Roman context Paul is having to deal with in Asia Minor (including Corinth), each school is a sort of cult of personality more-or-less in competition with other schools and their founders. (Somewhat similar to how East Asian martial arts represent distinct philosophical schools in their fighting!) Paul hates the idea of this kind of thing getting started in regard to Kephas, Apollos and himself, especially when the result is that “Christ” becomes one of the ‘factions’. (As he ironically quips, it’s a good thing he didn’t baptize any of those people!–otherwise they might think they were being baptized into his salvation!) The SSG has gone right outside even that grouping, though; which is why St. Paul keeps talking derrogatorily about “philosophy” in the first six chapters. (Paul can be shown to be a sort-of fan of Epictetus himself; and indeed quotes him vs. Epicurius as an ironic retort in chp 15! In case you hadn’t heard, in that famous speech at the Mars’ Hill forum in Acts, Paul is referring to the founding myth of the forum, which involves Epictetus the Cretan acting as a distaff ‘prophet’ of the Unknown God. But Paul absolutely refuses to consider himself a follower of Epictetus in comparison to Christ.)
The SSG’s sleeping with his stepmom, in any case, looks to be the means by which Paul is going to undo him and his influence in the Corinthian church: even the Gentiles in Paul’s audience have to agree that the SSG is doing something immoral by their own traditional standards, and his relativistic ethical philosophy be damned (so to speak. 
) The “destruction of the flesh” in this context probably means a veneral disease. (It’s still being done for the salvation of the SSG’s soul, in the day of the Lord to come, of course.)
Anyway: I take it that the reasons the SSG gets especially called out for zorching, are: 1.) he keeps persisting at doing what he’s doing; 2.) his factionalizing isn’t even within Judeo-Christian authorities (as bad as Paul considers even that); 3.) his teaching is actively corrosive to the ethical behavior of Paul’s congregation in the broader sense; 4.) he’s depriving them of Christian hope by teaching against bodily resurrection (or maybe even resurrection at all) of believers who have died (interestingly, St. Paul never says that the problem-maker(s) behind chp 15’s correction is denying that Christ was resurrected–Paul specifically contrasts the disbelief of some of them in resurrection-generally with their professed belief in the resurrection of Christ specifically, pointing out that it’s ridiculous to deny it generally but believe it specifically); and 5.) the SSG made the tactical error (so to speak) of doing something that even pagan Gentiles would regard as ethically condemnable.
So it’s a more complex situation than simply ‘factionalizers out, other sinners can stay’. 
None of which is to deny that any sin excludes us from being inheritors, so long as we insist on retaining that sin. That’s one of the key points to St. Paul’s ironic setup and follow-through in the first couple of chapters of his epistle to the Romans. Sure, those nasty pagan homosexuals have it coming (Paul is more charitable to them, on a careful reading, than might be noticable at first glance, but his subsequent point wouldn’t fly if he wasn’t being serious about denouncing their sins as really being sins); but having gotten his audience to agree (using an example which the widest majority of his audience would find repulsive and so easily condemnable) that those sinners have it coming, Paul starts weaving ‘little’ sins into his subsequent continuing list of ‘big’ sins: the upshot being (as Clint Eastwood’s “William Munny” grimly answers the Scofield Kid near the end of Unforgiven), we’ve all got it coming. So we’d better not dismiss or deny the mercy of God for those other people, no more than we hope and expect God to have mercy on us.
I’m a big believer in purgatory (though not the Roman Catholic model); but I would rather point out that any supernaturalistic theist who affirms salvation by grace, has to affirm that this grace operates post-mortem. It isn’t as though we could become self-existent independent facts, no longer dependent on God for our existence, if only we could die!
We exist and live and move and have our being and continually cohere, pre-mortem, thanks to the grace of God. The same is true post-mortem, too.
Even our sinning can only occur by the grace of God, in many ways. It’s an abuse of God’s grace; which is another reason why any sin is so heinous. But in a very real way, sin occurs because God loves sinners, too. He doesn’t love their sin; but He does love the sinners.
In regard to church discipline in GosMatt: I would say that not everyone being rebuked in 1 Cor are at the final stage; whereas the SSG was judged by Paul (under God) to be at the final stage.
In regard to 1 Cor 5:9-12: the same list (with some more detailed expansion in regard to sexual sins) is repeated in 1 Cor 6:9-11, with the reiteration that these shall not be “enjoying the allotment of God’s kingdom”. i.e., so long as people do these things, they will not be inheritors. 6:12, however, points out the distinction of those who have repented of such things and are being justified in the name of our Lord Jesus Christ and by the Spirit of our God. The difference is between those who are cooperating with God against their sins, and those who are persisting in their sins. God intends for the latter to inherit, too; but God would Himself be irresponsible if He let them inherit while they themselves insist on being so irresponsible. The social concept here, is that the father pays the redemption price of raising his child to the status of an inheriting son or daughter, who is given responsibility and authority to cooperate in the family business and to represent the father and the father’s name. The child doesn’t really stop being a child by behaving in a way contraventive to the character of the parent, but neither is the child going to inherit!–moreover, such rebellion reaches a point where the child effectively denies being a child of the father, perhaps joining up under the authority of someone else as a rival to the family.
The rebel child may insist on having it both ways, but that is only another quasi-convenient lie; and it isn’t one that the other children (much less the father!) are obligated to always permit the fostering of. True love doesn’t stop loving by saying “enough” and drawing a line, but the immediate form of the action of love is going to change in some (maybe even many) regards at that point.
This Greco-Roman (and Judaic, Near-Middle-Eastern) social analogy is very commonly referenced in the NT, both in the Epistles (especially the Paulines) and in the Gospels (both GosJohn and the Synoptics), as a way of helping illustrate the relationship between God and His own rebel or faithful or penitent children. Our cultural references have largely changed since then, so we modern (and relatively modern) readers don’t always recognize the analogical applications being referenced; which is why we often interpret ‘adoption’ in line with our truncated relatively-modern meaning of the concept, for example. Even good and natural children of 1st Century Mediterranean life were ‘adopted’ by their true father, though: it was the father’s way of acknowledging that the children had matured enough to take a responsible role in the family now, especially in regard to the actions of the family in the world.
That level of complexity explains a lot of the already/not-yet situations in the NT, including on the topics you’re asking about.
JRP
) Yet He had already been sending them out as ambassadors of the kingdom and of the King, and was about to do so again (preparing the way for His final tour through the Galilean, Samarian and Judean regions, plus that Arabian area east of Jordan at the Beth-Araba fords near Jericho.)
(The Greek is very emphatic there, too…!) The One Who is without sin, will be the one to throw the stone, sooner or later. He is the one Who can most be trusted to be fairest and most loving about vengeance. (“Vengeance is Mine; I shall repay!” says YHWH in the OT.) But there is a vengeance on the way, if we insist on having it. Including on those of us who profess accurate Christian truth and even who serve Christ, doing good and miraculous deeds in His name.
It is indeed a terrible thing to fall into the hands of the living God; but the living God is still the living God, and it is in the living God that I put my hope of salvation from sin and from my sinning.
