There has been a good series of posts on the Orthosphere recently on the subject of universalism and whether all will eventually be saved. One of them is here. They reminded me that I had written something on this subject a few years ago (here and here) which brought forth some interesting comments so it is clearly a subject that concerns people as well it might. Inevitably, no conclusion is reached in either case but the potential contradictions between perfect love and perfect freedom are explored.
For this is what it comes down to. God is a God of mercy and justice but in a conflict between the two which takes precedence? Since God is perfect the answer must be that neither takes precedence and both are fully satisfied, but how can that be? For us it is not possible but with God, as we have been told, all things are possible. One way for the demands of both to be met is that the soul is granted an indefinite period of time to get it right. This might require something in the nature of reincarnation and karma but that is rejected by Christianity, and though there are hints of it in the New Testament (for instance, reaping what you sow, the idea that John the Baptist might be Elijah come again, and "did this man sin or his parents that he be born blind?"), they are inconclusive to say the least. I personally am sympathetic to reincarnation as something like an evolutionary mechanism but it does focus on the theosis side of the spiritual path and ignores, or certainly downplays, the significance of salvation. I believe both are important.
Another possibility would be that purgatory is not just to purify the already saved of residual sins so that they are worthy to enter Heaven, its acknowledged objective, but also has a salvific aspect. Or, if we don't call this purgatory, there are forms of post-mortem existence that have this function. This would also be contrary to orthodox teaching which insists on the right choice being made in this life even if it is at the point of death. That's because there is something unique about life in a physical body as regards making a choice in complete freedom, a freedom that does not exist in the spiritual (meaning non-material) realm, or not to the same extent, because it is not fully separate from God. Nevertheless, if we want God to extend his mercy indefinitely, and we do not accept a return to the physical world, we should admit the possibility of repentance after death.
Then there is the question of Hell and what it is. In one of the posts on the Orthosphere I commented as follows. Heaven is an opt-in destination so you must want to go there and behave accordingly. This would mean that anything that was not Heaven could then be seen as a form of Hell. Perhaps the mistake the universalists make is to see Hell as necessarily a place of eternal torment. That may exist but it may not be the default option for those who reject God. Hell may have many mansions too and many of these may be not too different to how this world is, all reflecting the varying degrees of God rejection and self-assertion to be found in human souls. But they are not Heaven.
I said in the comment that Hell as a place of eternal torment may exist but I am not persuaded that it does. From the eternal point of view, what may happen to the truly recalcitrant soul that refuses to turn round and accept the reality of God is that it gradually loses its life force. All life comes from God. The demons must steal life energy from those who have it because they can no longer get it directly. Evil is parasitical. This is a major reason for their need to corrupt souls. They can then harvest the low level energy produced, the energy of anger, hatred, lust or whatever, but eventually souls that cannot receive life from God will wither and die if they cannot steal it from elsewhere. Meanwhile they will be in a sort of Hell because Hell is separation from God but this may not be experienced by them as torment. It may even have its pleasures though these will not be spiritual or not properly spiritual. After all, we are separated from God (apparently not really, of course) even while in this world.
God obviously wants all souls to be united with him but this must be on a voluntary basis or it is coercion and that would negate the whole point of creating souls with free will who can, in their turn, add positively to creation. If a soul fails the test of turning to God in an environment where that does require a choice (the material world) there are two possibilities. Either it is consigned (that is to say, it consigns itself) to the cosmic recycling bin or it is given new opportunities to get it right, perhaps here, perhaps elsewhere in quite different environments. The idea that it is tortured forever for the failure of a single finite life seems unreasonable, illogical and quite contrary to the idea of a God of love. However, like attracts like in the spiritual world, and for as long as a soul rejects God its consciousness will remain endarkened which is a kind of hell though may not be experienced as such by the soul that has adopted this position. I believe we need to see post-mortem conscious existence as containing many levels. It is not just black (Hell) or white (Heaven) but there are many shades in between. If we see Hell as anything that is not white we may be closer to true understanding. Perhaps jet black Hell is the one place from whence there is no return but most souls who fail to attain Heaven go to some kind of grey hell and from these there is possible redemption. Black Hell is for full and final God rejection but for those who may not have reached this tragic depth there remains hope.