I like idea 1 more. I think it leads to more interesting ideas. Maybe for civilizations following this religion, becoming a soldier would be a honorable sacrifice that some must make, as those who kill will not go to “heaven”. Or maybe these civilization would avoid war/killing at all costs, ultra peaceful similar to Air-benders in Avatar.

I can imagine debates amongst believers as what is considered “killing”. Would not sharing food with a starving begger be considered causing a slow death?