Heaven, increases all feelings to their extreme quality. Hell, decreases all feelings to their minimum quality. So if someone dies feeling sorrow, rage, hate and goes to heaven they’re going to feel all those to their extreme, that is why god creating hell is actually an act of love because he wants us to feel sorrow, hate, rage as little as possible and feel love to its extreme.
There’s no scriptural references I know of off the top of my head about increasing and decreasing feelings. But if you have some, please share.
Because God is all perfect, so God is all loving, but also perfectly Just. A loving God would set the reward to be to bring His children to him, but imperfect children cannot be in His presence, as God is also perfectly Just, so sin needs to be punished. Because sin transgresses God greatly, it cannot be erased by doing the right thing. We always have to do the right thing regardless. You cannot make a fine for running a red light go away because you stopped at the next three red lights. You need to pay with something above the road- driving. So the payment for our sin is above this world.
God is all loving, so 2000 years ago, he became incarnate as a man and lived as one of us. He ended up suffering, dying and He was buried. He lived a perfect life - the life we should have lived. Yet he died the death we deserved, and descended into Hell for three days. A perfect sacrifice was made. Now, all heaven requires is simply renouncing our allegiance to sin and turning it back to God.