Like most eschatological things(*), the fate of the lost is just vague enough that it's great place to raise dust without settling anything.  There are two main problems: first, the Scriptures don't have a lot of details, and the ones they have don't fit together in a simple way; and second, the whole subject is so horrendous that it's hard to stay calm long enough to think it through.

To get the doctrine out in the open: the predominant view throughout Church history has been that by our sin  we have all rebelled against God, so that we are under His judgement,and if nothing saves us, every one of us is headed for everlasting conscious punishment in Hell.  Sounds bad.  Let's look atwhat this doctrine means, why it's held, and what the alternatives are.

Retribution in the next life for wrongdoing in this one is not a specifically Christian doctrine; it's common to almost everyone who has thought seriously about the moral law and the immortality of the soul.  The ancient Greeks thought that spectacular sinners went to Tartarus, a place of everlasting torment; the Hindus think that we are reincarnated into a body that reflects the balance of our good deeds against our bad ones. There's an obvious discrepancy between what people get in this life and what they seem to deserve.  If there is justice in the universe, this has to be made up at some point; if not in this life,then in the next.  The two specifically Christian things are that everyone, not only the worst, is under sentence of condemnation; and that Jesus Christ, by His death and resurrection,has broken all our chains and offered all of us a way out,scot-free.  Thus the sentence is universal, and yet nobody need suffer unless they choose.  This is the ultimate bad news and the ultimate good news.

Let's come back to the point about justice for a minute.  The idea that a good God would inflict infinite punishment for finite wrongdoing is so monstrous on the face of it that it makes us squirm.  Even on sober reflection it doesn't seem reasonable, so people have tried various ways to make sense of it.  The thing that we must not do, if we take Jesus seriously, is to deny that some people are eternally lost, because He emphasized it in the sharpest terms.  The soul's choice is between everlasting life with God, and everlasting separation from God.  That separation is what we call Hell.

Hell is not somewhere under the ground, and it doesn't have red guys in tights with pitchforks.  God is not a vindictive tyrant, but a loving Father.  The language about lakes of unquenchable fire, undying worms, and so on is a symbolic attempt to describe the indescribable, to give an idea of the badness of Hell as harps and gold streets give an idea of the beauty and bliss of Heaven.  Hell is an alarmingly real place,prepared for the Devil and his angels; what we can legitimately disagree about is its human population.

Christians ought to cherish every possible hope for the salvation of each individual:charity requires no less.  The question is whether we can hope that everyone without exception is saved, which is quite another thing.

Ordinary justice requires that wrongdoing be punished, and that punishment should fit the crime: the worse the crime, the worse the punishment ought to be.  Saint Thomas Aquinas usefully distinguishes two kinds of pains of Hell: the pain of sense, which is the punishment, and the pain of loss, which is the everlasting separation from God.  In his view, God inflicts the pain of sense in the amount required by justice, which is always finite, but the pain of loss is something an individual freely chooses by rejecting God, and is infinite because it lasts forever. 

In this life, the sin itself is a great part of the punishment of sin; perhaps the pain of sense is merely the result of coming face to face with God, rather than something God positively inflicts.  Scripture says that God does not desire the death of the wicked (that is, their damnation), but desires that all should repent and be saved instead.  Thus no one at all need go to Hell. 

At present God is invisible to us, which is why we are free to make up our own minds. God's visible presence is so overpowering that there will be no opportunity to accept or reject Him when we see Him—instead we'll find out what we have already chosen.  When we see Him face to face, His presence will be to us overwhelmingly beautiful or overwhelmingly terrible, depending solely on our earthly choice, and until then it isn't necessarily obvious which way we have chosen.  That's why Christians are so concerned with people's faith here on Earth. 

Hell is God's best provision for those souls who are not able to endure His presence.  He has set His image on each of us, and desires that we should all freely choose to be united with Him forever.  However, our freedom is real; we are free to embrace sin instead, and by so doing, damage ourselves so badly that His presence is intolerably painful. Jesus tells us that some people do so.  He cannot make them happy without Him, for such happiness does not exist.  What He can do is to put a limit on their self-imposed suffering by removing Himself from them-which of course is His last opportunity to show mercy towards them.  That state of being separated from God is what is called Hell.

Some people find this mainstream view incompatible with their idea of God, and so two alternative views have arisen.  The first is universalism, which essentially says that the goodness of God is so attractive, and His grace so wide, that no one can refuse it, and so everyone will be saved in the end.  This view will  be sufficiently criticized in other posts, but briefly, it fails to take Jesus' words seriously, and does not explain why the Apostles and the early martyrs let themselves be killed one after another, rather than deny Jesus—surely a very odd thing to do if no one's salvation was at stake.

A middle-of-the-road alternative is annihilationism or conditionalism, a picture in which the lost souls simply cease to exist, possibly after being resurrected for judgement and punishment. 

Both of these views are very old,dating from at least the third century AD.  Origen (d. 253 AD) was a universalist at one time, but not one the moderns would recognize: he thought that the unquenchable fire was purgative, and that after long ages of pain the soul would ultimately be purified and go to Heaven.  Arnobius (early 4th C) saw the lost as being gradually consumed and annihilated by the unquenchable fire, so their suffering didn't last forever.

The modern universalist and annihilationist views are much less respectable, because they usually edit out the pain altogether.  This would be nice, but unfortunately it isn't true. To get there, one has to replace scriptural authority with wishful thinking.  Both these views fundamentally fail to satisfy justice, which is a primary value of all humanity, and an unalterable attribute of God.

Being superficially so attractive, annihilationism is much easier to defend in a popular discussion than everlasting conscious torment.  In 1 Peter,Jesus is described as preaching to the 'spirits in prison'. One can argue these spirits were being punished before being allowed to vanish; that would accomplish justice, but it seems pointless—why preach to people who can no longer repent? One can also argue that souls are not intrinsically immortal: we each have a quite definite beginning, so why not an end as well?  There's a lack of scriptural evidence in favour of this view, though, and several Dominical sayings raise serious problems for it: the rich man and Lazarus (Luke 16:19-31); the sheep and the goats (Matthew 25:31-46); casting the lost into the lake of fire(Revelation 20:15); the fire that is not quenched and the worm that does not die(Mark 9:43-47, quoting Isaiah 66:24); and so on.

The reason all this is so difficult is that not that the theology is so hard but that very deep feelings are involved.  Teetering on the edge of the abyss is a nervous position.  We don't like to think of ourselves or people that we love perhaps being damned; there's a strong temptation to react violently against the idea, and possibly against those who defend it.  We can all understand the feeling, but it's cruel not to tell the truth.  

My own mother became a Christian five days before she died, having rejected Christianity as a young woman.  Until that day, though I was heartbroken about her dying, I was far more afraid of her possibly being lost.  Many of my other relatives and friends are also not Christians, and I would be able to take a much more relaxed view of my duty to tell them about Jesus if I knew they'd be saved in any event.  We have to be merciful to people who can't accept the reality of the situation we're in, but we have to be clear ourselves.  It's like the denial of death; we find the idea intolerable, so we may try to rationalize it away.  This is all very human, but it leads to disastrously bad decisions.

We so easily imagine that we are more merciful than God, and we are often willing to abandon justice in so doing.  We want to argue like this:

1.  Imposing infinite punishment for finite wrongdoing is monstrously unjust.
2.  God is good.

Therefore,

3.  There is no everlasting conscious torment in hell, or better, no hell at all.

The simplest orthodox reply is that both premises are perfectly right, but that the conclusion doesn't follow.  The key word is "imposing".  God imposes finite punishment, some in this world, some in the next, in accordance with His justice.  But the infinite part is the lost soul's own doing; it follows from finally rejecting Him.  God died to prevent us from suffering infinite loss, by freely taking our guilt and pain on Himself; it is a free gift of grace, but one we are free to refuse.  Asking God to let the wicked off without repenting is the same as asking Him to pretend that sin does not exist, to pretend that people who have finally rejected Him could be happy in His presence.  They can't, and He can't—though He wishes He could (Matthew 23:37 ).

Another way out that doesn't work is to say that the mainstream view implies the unfair damnation of very good people—Jews, or Muslims, or Hindus, or cave men, or atheists, or whoever, and then say that since this is obviously unfair, the whole doctrine is discredited.  We'll have more to say on this topic, but no Christian is required to believe that all non-Christians are damned, any more than we believe that all Christians are saved.  Christ is the only name by which we can be saved; we know that those who finally reject Him are lost, but we don't know who they are.  The Bible specifically says that there are people who don't know God who are still saved, though the implication is that such salvation is uncommon, and certainly shouldn't be relied upon. (One or two people have survived falling from an airplane with no parachute, but it's a lot safer if you have one.)

Saying that the lost go to Hell is not the same as saying that any particular individual has gone there.  Few hearts are more desolate than a Christian's, when a loved one dies as an unbeliever.  This is a much worse feeling than ordinary grief.  To those, we have to be ready with hope; God is good, and Hell is harder to get to than they may think.  We have good grounds to hope for the salvation of anyone, even those apparently most abandoned; we don't know their hearts.

We may sometimes be tempted to wish that Hell were easier for some people to reach. This temptation has to be strangled at birth, because wishing someone damned is about as evil a sentiment as the human heart can contain.  Jesus commanded us not to judge each other—we are to judge actions, but not people; to hate the sin and love the sinner.  We therefore have a duty to hope that each individual may be saved, but that isn't the same as being able to hope that everyone without exception is saved.  This isn't logic-chopping, it's what we always do when there's a disaster.  We may know that people have been killed, but we still hope and pray for the safety of individuals until the full truth is known.

And this is really the position we're in: we are uncertain, so we must live by faith, hope, and charity; neither sinking into despair nor sliding into complacency, but staying awake and helping others to stay awake too.

———————————-

(*)  i.e. having to do with the end times and the Second Coming of Christ