Nameless – I fear you have made some more mistakes, gehinnom is at most, a year, unless you did one of the things you dont get out of gehinnom for(even then it’s not eternal, just very long), this is why we say kaddish for 11 months, to be dan lechaf zchus that it wasnt a year, since only a very bad person would get a year, so we do it for 11 instead of 12.
Because hashem is a baal rachamaim he punishes us. This is because gehinnom is a chessed, it’s a way of purifying is for gan eden – this is where we enjoy our maysim tovim and mitzvos, however, as I said before, the reward for mitzvos is 500 times greater than the punishment for aveiros, so it would not be fair to have them cancel out aveiros – it would mean less reward for you.
Also, teshuvah erases mistakes while you are still alive – not after you’re dead, so the idea of erasing misdeeds works even when there is a moment left to life. Once you’re standing for a judgment though, there is no teshuvah – otherwise, no one would go to hell at all, plus, the purpose of life is action, oth good and bad, changing the self – olam haba is stagnant, it has nothing to do with growth, it is what you make it, literally.
Now, I cannot say kol kevudah(the pushut pshat) is a lav, but it is halacha, and is used in halacha all throughout shas and poskim.
I do not remember which mussar sefer disucsses your misconception about din vecheshbon, but I am sure I have seen it addressed as a misconception, i think it was the nefesh hachaim, but i honestly do not remember now.
The story of that baal teshuvah was said over at the shabbos table – it’s a touching, beautiful mayshoh, but I do not what relevance it has to what we were discussing – that man came back, and hence, he did teshuvah, but he would not have been able to do that if he stayed there, as he said himself, all the malachim he made with his averos were there, and once you’re in beis din, there’s no teshuvah anymore – thats only something you can do here, and here, he did it, thank G-d.