I see two things as sin, trying to kill god and denying your "self". Denying yourself, as you are part of god and god is in you, is like trying to kill part of god. So this is trying to kill god through yourself.
Likewise when people hurt people when not for vengeance or self-defense, or hurt animals when not for food or self-defense, this is denial of Self through the person, which is like-wise like trying to "kill" god.
But killing god is impossible as he is the Universe, so in reality True evil is impossible. To truly commit evil would to be to end everything. So in essence sin is a temporal thing. Most of the time people can fix this by "acceptance of self" in the case that the crime is committed against yourself. if it's committed against someone else, then you have to make it right with them and have them forgive you OR they can make it right by getting their vengeance. Either way will work.
The only real long-term consequence only occurs when a bunch of sin builds up, and it damages our souls. Our souls are different than our spirits. The soul is the living part of our spirit that is part of our flesh, or in other words our personalities and egos. When most people die their souls die, but their spirits break-up into wisps. So I guess a lot of un-paid (not forgiven or vengeance taken against) sin would make the soul less likely to cling to the spirit on death. So if someone lives a life of hurting others for no good reason, then it stands to reason that when they die that's just that. For those who's souls stay more or less intact after death, they get to become either gods or lesser entities.
But even for those people the death of the soul and the breaking of the spirit into the elemental pieces is more like the deepest of deep slumber, where you have no conciousness, and no dreams. So what is left of the core piece of the spirit still exists and experiences, but the sin filled person really doesn't suffer a whole bunch in the end.