The thing about hell, like many other doctrines, is that on its face it seems entirely illogical, inhumane, and downright evil. That is, devoid of context, it looks incredibly cruel. It's a bit like trying to explain the doctrine of predestination. You can't simply start with predestination itself because the reason for its existence stems from other doctrines. The same is true for Christ's redemptive work on the cross. I've heard some people call it divine child-abuse, as though it were not only evil and unjust, but entirely unnecessary. The doctrine of hell is no different. The nature and reason for its existence is predicated on other realities.
Traditionally, the doctrine of hell refers to the eternal damnation for the reprobate. The keywords surrounding the controversy are eternal and reprobate. For the latter word, the debate usually entails the question of whether God would even send anyone to hell in the first place, if it even existed. The former is the question of whether hell is suffered for a finite period of time, and if those who suffer it are eventually annihilated or redeemed. There's also the question of the nature of hell itself. Is it a place where God's wrath is poured out on the unrepentant, or is it a situation that we create for ourselves when we don't order our lives as God would like? There are at least as many views of hell as their proponents, but they usually fit into one of a few streams of thought. And although they may be historical, that doesn't mean they're historically orthodox.
Today's cultural ideals of pluralism, tolerance, and even democracy and fairness, have caused an increasing number of people to question the legitimacy of Hell's orthodoxy. The topic of hell has been, well, hot for quite some time now. The controversy over Rob Bell's new book, "Love Wins" is indicative of current cultural climate. At any rate, whatever camp you find yourself in, what you believe about the Hell speaks volumes about what you believe about a great many other things, not least of which is your view of God's love. That's because the doctrine of hell is so inseparably intertwined with other doctrines. You cannot divorce it from God's other attributes.
Let's be serious about one thing though. The usual alternatives to hell (i.e. universalism, annihilationism) from as early as Origen or Gregory of Nyssa have never been accepted as orthodoxy. From the earliest of creeds, to Rome, to Eastern Orthodoxy, or to Protestant evangelicalism, these views of always been rejected outright. They've never passed the rigours of proper exegesis, and their arguments have always fallen flat, regardless of how attractive they may seem. To include them as sound doctrine doesn't mean expanding the borders of orthodoxy, it means moving them somewhere else entirely. More importantly, however, if you don't like the traditional view, your quarrel is not with the theologians who argue for it, but with Jesus himself. Jesus talked more frequently, more seriously, and more earnestly about hell than any other person in Scripture. And let's be honest, for someone who went through it, why wouldn't he?
My suspicion is that a lot of people cringe when they hear about hell not because it's in Scripture, but because people who endorse it have often abused it. The BBC once featured a documentary called, "The Problem of Evil" based on the works of the atheist and Oxford University biologist Richard Dawkins. In it was a segment that showed a pastor of a church deep in America's Bible-Belt who would put on plays about how awful hell was. The whole idea of it was to (quite literally) scare the hell out of the youth group kids so they would turn to Jesus. While people can come to a knowledge of Christ after learning about only about hell, a presentation like this served as nothing more than a blatant abuse of power. Kids would repent out of fear of reprisal, not out of a genuine understanding of God's infinite grace. Jesus is a sort of "fire insurance" if you will.
But for those who struggle with hell because it confronts them in Scripture, the first problem is its awful nature. As Tim Keller notes, the idea of hell-fire is probably metaphorical. That is to say, it's probably metaphorical for something far worse. We cannot escape the Biblical descriptions of hell. It really must be that bad, and for all we know, it could very well be even worse.
To some, however, this creates a problem of theodicy. How could a good and loving God possibly send someone to hell, if not for a short time, but eternally? But this isn't a question of God's love, it is a question of God's justice. If we believe God to be perfectly just, then it must follow that what befalls those going to Hell is befitting of the crimes committed. On the other hand, if a hell like this is simply too severe, then either our sin isn't that serious, or God is unjust. An unjust God is a God who, in the end, provides no hope for those who put their trust in him. In fact, he cannot be trusted in the first place. So it must be a question of the seriousness of sin.
Is sin so bad then? Imagine if Jesus himself made the slightest of slips on earth. Imagine if Jesus himself gave into the temptations of Satan. Imagine, if even for a moment, Jesus decided it wasn't worth the pain, everything that he had set out to do on Earth would've failed. At the end of the beatitudes, Jesus declares with finality, "...be perfect, as your Father in Heaven is perfect." That is the standard by which Jesus had to live. Thank the Lord, Jesus did. In the face of an infinitely good God then, the insult of sin is infinitely serious.
And why is it eternal? The answer to that is as simple as it is profound. It's because our very nature dictates it. Some people depict hell as being unjust, as though people in hell are clamouring to get out, begging for mercy while an insidious and sadistic God throws them back in. The problem is, they may look for an escape, but it's not out of a repentant heart. The story of the rich man and Lazarus depicts this better than any other story. The rich man has absolutely no acknowledgment of his sinfulness. Having entered hell, the sinning doesn't cease, it carries on like an addiction that endlessly spirals further and further into a bottomless pit. C.S. Lewis describes it this way...
Hell begins with a grumbling mood, always complaining, always blaming others . . . but you are still distinct from it. You may even criticize it in yourself and wish you could stop it. But there may come a day when you can no longer. Then there will be no you left to criticize the mood or even to enjoy it, but just the grumble itself, going on forever like a machine. It is not a question of God 'sending us' to hell. In each of us there is something growing, which will be Hell unless it is nipped in the bud.
(The Great Divorce)
So what about the charge that this somehow denies God's love? Hell does not, in any way, take away from God's love. On the contrary, it strengthens it because it demonstrates how deep and powerful it is. At the heart of Christianity is a God who suffers for us, and has become victorious for us. It's one thing for a man to go through hell deserving it. It's an entirely different matter when someone so obviously perfect goes through it voluntarily in place of the other. Perfect justice, then, does not demean love. It makes love all that much more profound. Both God's love and his justice are fully satisfied through Jesus Christ, and is continually satisfied for us.
Does God, in the end, save us all? The Bible clearly says no. But this too does not make God any less just, even if he had chosen just one person in all mankind to be saved. We all deserve to be wiped out in the flood, to never return to Eden, and be cast away. To us, it's not fair. But to be fair, God would just send us all to hell. It's the fact that he has mercy on any of us in the first place that's so amazing. So it's not a question of how God could send anyone to hell, but how he would bother to redeem anyone at all.
Again, as C.S. Lewis writes
In the long run the answer to all those who object to the doctrine of hell is itself a question: ‘What are you asking God to do?’ To wipe out their past sins and, at all costs, to give them a fresh start, smoothing every difficulty and offering every miraculous help? But he has done so, on Calvary. To forgive them? They will not be forgiven. To leave them alone? Alas, I am afraid that is what he does.
(The Great Divorce)