Re: if we knew of our death ahead of time.
I want to add a non religious aspect to the discussion here.
Let’s assume that we were to only live till eighty, a hard universal fact for every human ever.
I believe that people would be more productive. They would be getting married earlier, higher education programs would be of shorter length and people would be becoming doctors and engineers at younger age. There might be less greed in the world and more vision of doing something to help coming generations.
Legal system might be different. First of all, there might be less crimes (because of less greed maybe). Second, we would be more of an instance justice society as giving long term imprisonment to older folks would be meaningless, which means that our punishments would be harsher (result of instance justice), which would result in less crimes.
Medical advancement would be there, but people would be more focused towards quality of life vs quantity (living longer).
This is rather a very simplistic viewof human behavior knowing time of death specially when you take religion out of equistion. I see things quite opposite.