How Far Is Heaven?

I just want to know, when did religions have to write in the rule that you couldn't run off and kill yourself to get to the grand reward (be it Nirvana, Heaven, etc.) so that the devout in horrible situations, such as extreme poverty, slavery, and serfdom (especially serfdom, it seems like the Catholic church, and later many of the Protestant denominations were built on keeping the serfs in their place with the carrot of having a afterlife worth living in servitude for).

I'm not familiar enough with Bible verses to know what verse tells you not to off yourself less you go to meet the devil, not live in the clouds, and of course in some places there's the misguided thing about killing yourself as a way to get vengeance on others - but there your performing a service - for people to cowardly to do it themselves. Instead heaven must be achieved by most by accident, by someone else's hand, or by natural causes.

Still, if it weren't for the "rule" don't you think there'd be more people trying to get to heaven than there are now?