If someone truly believes that they could face either an eternity of joy and bliss or an eternity of suffering and pain, based on adherence to some religious precepts for less than a century... well, which is more "important" gets a bit fuzzy. At first, the part that will last for eternity is more important. You could literally sleep through this life and it wouldn't make a blip in your eternal existence. However, if the entire scope of your eternal life is going to be based on what you do here, then this seems to be the more important part.
But either way, if such an afterlife exists, then we would be insane to do anything other than devote our every waking moment to ensuring that we go to the good eternity and not the bad one. Though I suppose that depends on how hard it is to get into heaven.
We'll assume the Christian heaven because it's more well known and Judaism is kind of fuzzy on afterlives anyway. So, obviously, you don't get in if you're the wrong religion. Fine, so our hypothetical person is a Christian. Does it matter which denomination? A lot of denominations say so, so we also need to make this person the right denomination. I don't know which one that is, and if they contradict each other and proclaim that the others aren't really enough and go to hell (like they did a lot during the reformation), then you have to spend your life figuring out which one it is. This is, of course, after spending your life figuring out if Christianity or Islam is correct.
So then next we have the major sins that you can't ever do. Obviously, the more violent ones are easier to avoid. But what about the internal ones? How much coveting is okay during one lifetime? How many lustful thoughts are you allowed? Does premarital sex automatically send you down the hole? Some people think so, some don't. Gotta figure out which it is, and probably shouldn't have any sex at all until you do. Probably should do everything you can to avoid even thinking about sex. Obviously, you can't be gay.
I actually don't know much more than that about the rules about who does or doesn't get into heaven in any major denominations of Christianity. I don't know what the limitations are on confessing in Catholicism. If you manage to confess all your sins before you die, are you good to go no matter what? Assuming you don't kill yourself or get excommunicated? I don't know how Protestants balance everyday acts of douchebaggery against... whatever makes up for that. Exactly how much of a jerk can you afford to be before you lose your place? Say a man beats his wife exactly three times during his whole life. Is that too much? How about beating up a smaller kid in school? How about getting into a car accident because you were drinking and injuring, but not killing, another person? Where actually are the limits?
If you really believe that there is a forever or joy or of misery on the line, a person should spend their life with no goal in mind other than ensuring that they get the good ending. Because a century means nothing compared to an eternity. I honestly find it very strange that religious people don't act this way. Apparently it was more normal back in the middle ages. Maybe Paleocon actually operates like this. But I've never met someone face to face who did. People who claim to have an afterlife ahead of them seem to be pretty cavalier about it. Maybe the threshold is really that low?