A “just” God does justice, which means to punish or reward appropriately. In the Western tradition, we punish people for the actions they commit, but the extent of punishment is dependent also on the person’s mental state, and a person’s mental state is reflective of his or her beliefs. Premeditated murder is worse than manslaughter, and is punished more severely, and a hate crime is a sentencing enhancement that adds more punishment to the underlying crime. In both examples, a person’s beliefs are at play: the premeditated murderer has reflected on his choices and wants the victim dead; a hate crime reflects a belief that the rights of a member of the protected group are especially unworthy of respect. So, considering a person’s beliefs may well be relevant, especially if those beliefs have motivated the criminal behavior.
But the challenger’s mistake is even more fundamental. He is wrong to assert that people are condemned for not accepting the gospel. Christians believe that people are condemned for their sinful behavior – the “wages of sin is death” – not for what they fail to do. The quoted challenge is like saying that the sick man died of “not going to the doctor.” No, the person died of a specific condition – perhaps cancer or a heart attack – which a doctor might have been able to cure. So too with eternal punishment. No one is condemned for refusing to believe in Jesus. While Jesus can – and does – provide salvation for those who seek it, there is nothing unjust about not providing salvation to those who refuse to seek it. After all, we don’t normally feel obliged to help someone who has not asked for, and does not want, our assistance. So too the Creator has the right to withhold a gift – i.e. eternity spent in His presence – from those who would trample on the gift, and on the gift-giver.
The quoted assertion also demonstrates an unspoken belief that we can impress God with our “kind” or “generous” behavior. This fails to grasp what God is – a perfect being. We cannot impress Him. What we do right we should do. We don’t drag people into court and reward them for not committing crimes. This is expected of them. They can’t commit a murder and then claim that punishment is unfair, because they had been kind and generous in the past. When a person gets his mind around the idea of what perfection entails, trying to impress a perfect Creator with our “basic goodness” no longer seems like such a good option.
Here’s a related answer from CARM. This one answers the question about degrees of punishment in Hell.
Yes, there are different degrees of punishment in hell.
[...]But, not all people are equally bad. Though all deserve damnation because all are sinners, different people have committed different degrees of sin.
- Mt. 11:20-22, “Then He began to reproach the cities in which most of His miracles were done, because they did not repent. 21 “Woe to you, Chorazin! Woe to you, Bethsaida! For if the miracles had occurred in Tyre and Sidon which occurred in you, they would have repented long ago in sackcloth and ashes. 22 “Nevertheless I say to you, it shall be more tolerable for Tyre and Sidon in the day of judgment, than for you…I say to you that it shall be more tolerable for the land of Sodom in the day of judgment, than for you.”
- Luke 12:47-48, “And that slave who knew his master’s will and did not get ready or act in accord with his will, shall receive many lashes, 48 but the one who did not know it, and committed deeds worthy of a flogging, will receive but few. And from everyone who has been given much shall much be required; and to whom they entrusted much, of him they will ask all the more.”
- John 19:11, “Jesus answered [Pilate], ‘You would have no authority over Me, unless it had been given you from above; for this reason he who delivered Me up to you has the greater sin.’ ”
- Heb. 10:29, “How much severer punishment do you think he will deserve who has trampled under foot the Son of God, and has regarded as unclean the blood of the covenant by which he was sanctified, and has insulted the Spirit of grace?”
So, if Jesus speaks of greater condemnation for Chorazin and Bethsaida than Tyre and Sidon (Matt. 11:21-22), one slave received more punishment than another (Luke 12:47-48), the one who delivered Jesus to Pilate has the greater sin (John 19:11), and a more severe punishment is reserved for those who trample underfoot the Son of God, then does not greater sin mean that greater punishment will also happen in hell? Yes it does.
Not only are there degrees of punishment in Hell, but there are degrees of reward in Heaven, based on what you do on Earth and what strengths you start out with.
10 I rejoiced greatly in the Lord that at last you renewed your concern for me. Indeed, you were concerned, but you had no opportunity to show it.
11 I am not saying this because I am in need, for I have learned to be content whatever the circumstances.
12 I know what it is to be in need, and I know what it is to have plenty. I have learned the secret of being content in any and every situation, whether well fed or hungry, whether living in plenty or in want.
13 I can do all this through him who gives me strength.
14 Yet it was good of you to share in my troubles.
15 Moreover, as you Philippians know, in the early days of your acquaintance with the gospel, when I set out from Macedonia, not one church shared with me in the matter of giving and receiving, except you only;
16 for even when I was in Thessalonica, you sent me aid more than once when I was in need.
17 Not that I desire your gifts; what I desire is that more be credited to your account.
18 I have received full payment and have more than enough. I am amply supplied, now that I have received from Epaphroditus the gifts you sent. They are a fragrant offering, an acceptable sacrifice, pleasing to God.
Everyone who believes in Jesus gets salvation, but your experience in Heaven will be different based on what you do while you are alive. And that’s also the answer to another common question – about deathbed conversions. Both deathbed converts and William Lane Craig will get the same experience of being in the presence of God, but there are completely different levels of reward. One Christian has an empty account, and the other Christian has huge massive amounts of virtuous, self-sacrificial action on deposit. One has experienced following and imitating Jesus very little, and the other one a lot.
Having said that, I think the real reason that Christians are trying to do good things here on Earth is that they like God, and they want to be his friend. They want to work on the relationship, even if it means a little self-denial, and a little sacrifice. We all have things that we would rather be doing for ourselves, but sometimes we have to things that work – things that are effective – for someone else. My values are not his values. Sometimes it is good to do something based on what He values. I don’t always have to get my way, because then it wouldn’t be a real relationship.
I enjoy thinking about Bible puzzles like this… so often in church we just make Christianity a checklist of things that we are supposed to believe somehow, by brute force willpower. I think reflecting on these problems, asking questions, and making sense of them on our own, is a much better approach.