A point with Christianity some people wonder about is the idea that even horrendous crimes will be forgiven when the party repents while unrepentant sinners, though their sins are minor, will be punished. This doesn’t seem fair. The thing is that it doesn’t make sense to select people for eternity based on particular actions in the few years we are on earth, which may depend on a lot of things beyond our control. Concerning morality, it is more about how our characters are progressing.
Take one example (and props to C S Lewis for this). Say you have three men. They are all prone to go into violent rages and want to physically harm people who annoy them in the slightest way. One is confined to a wheelchair and his violent rages only cause people to laugh at him. Another is a healthy, strong man and injures or kills a few people before being imprisoned. The third finds himself in charge of an air force and so can kill millions.
Human justice would rightfully judge the men differently based on their actions, but in the eyes of God it makes sense that they would be judged the same, with the difference in their actions merely stemming from their particular circumstances.
Take another example. You have two men. One starts out as impulsively violent in his youth but over time realizes the error of his ways, repents and changes. The other starts out mellow in his youth but becomes more bad tempered over time, but maybe this doesn’t result in violence because his testosterone and physical ability lowers with age. Human justice would judge the first man more harshly than the second, but with God it would make sense for it to be the other way around.