From my Catholic perspective...
Sin is separation from God. Sin becomes a habit, and a choice to not stand in communion with God. He allows free choice, and Hell is a place for those who do not wish to be with Him.
Is it hellfire and brimstone? Who knows - perhaps that's the way to describe the very terribleness of hell. I lean towards the idea that hell is the very despair, agony (physical and mental) and bleakness that occurs in very deep depression.
The older I get,the closer I get to God and the further I get from the worldly concerns of the frivilous and trivial.That is a good thing.
I went to a Jesuit college and have much respect for the academic rigors the Fathers instilled in us.I never became a Catholic but the denomination certainly played a role in me coming around to a pro-life stance in the Eighties.
Sin is separation from God.
This is well-stated. I'd add this: It's my experience that anything self-indulgant seperates me from my Higher Power, who I call God. Even things that might not normally be considered a sin seperate me from God -- the common theme is always acting out in Ego, or Self.
One of the quickest ways for me to get out of Self is to commit to, and be of service to others. If I ask myself "How can I best serve the person who is in front of me", I quickly get out of selfishness and self-centeredness. I quickly regain my conscious contact with the God of my understanding.
Is it hellfire and brimstone? Who knows - perhaps that's the way to describe the very terribleness of hell.
The aftermath of my very last 'using episode' was hell for me. I was disconnected from the girl I was dating at the time, I couldn't get my sponsor or anyone on my network, and my connection to God was shot-out. I was, utterly, alone -- and in great despair. That was sheer hell, but I am grateful for it, because it is what finally got me to live differently.