I dont, and really...neither does anyone else.
This so much. You just do what feels right. Most people can figure out right from wrong anyways just from their own upbringings. Parents/schooling give you a pretty good sense of right and wrong granted you haven't been failed in those areas. And if those areas fail miserably, then maybe religion can fill the gap.
What if it feels right for someone to murder and rape?
Religion isn't going to stop a psychopath from killing anyone, it's just going to make him justify it in a different way.
Let's say that it's 10 years from now. I've been kicked out of my foreclosed house, my wife has left me, and I have lost contact with all my family out of shame. I go to a local bar to drown my sorrows with whatever money I have left. You are a homeless man whom no one really knows. You save enough money to buy a lottery ticket. From watching a TV through a store window, you find out that the lottery ticket you bought is the winning ticket. You go to the same bar I go to that evening to celebrate. You haven't told anybody that you won and you wouldn't really know who to tell because you don't really know anybody and no one really knows you. Yet after a couple of drinks, you open up to me and tell me that you have a winning lottery ticket. As you start leaving the bar late night, I follow you. That lottery ticket could solve all my problems.
If morals were subjective / if I was a nihilist / if I was an atheist and I knew or was utterly convinced that I could get away with killing you and stealing that lottery ticket, what would stop me from doing so? Wouldn't it be beneficial to me to do so? I mean, after all, aren't we just a bunch of randomly ordered matter that will inevitably die and become more randomly ordered matter?
Wow, where to start...
First of all, you seem ot be completely unaware of who psycopaths are, what it entails, etc. Read through
this. Religion will be irrelevant.
Secondly, you seem to be completley ignorant of all the horrible atrocities committed in the
name of religion. You see, the thing about eternal damnation and eternal rewards is those two things can lead to some very unsavory and horrible ends. TO take your example, perhaps my religion honestly believes that that homeless guy getting the lottery is unjust, evil, and that he is an evil man. It then becomes my duty to kill the evil person. Or, perhaps as is the case in some religions, I'm supposed to "talk to God" personally, which basically amounts to listening to what you want, which could lead to me honestly thinking God wants me to kill that person, and for me to get the money. God set it up so that the homeless man would win, and come talk to me, to show me what I"m supposed to do. There's so many instances of this through out history, I won't even bother to list them for you.
Secondly, AS someone who doesn't believe in God, doesn't think God exists, and isn't afraid of eternal damnation or eternal bliss, I can tell you that my disposition and beliefs are completely abhorrent to the idea of killing someone for money. I could put this in a very selfish light, saying that I couldn't kill someone because that action would haunt me for the rest of my life, and I couldn't live with myself. And seeing as how I don't think I go anywhere when I die, I want this life of mine to be as good as possible, meaning I"m not going to kill someone and self-torture myself.
There's also the fact that, as I would contend, all you're doing by following religious teaching is following someone
elses moral compass, not even your own. You listen to the book, that some other guy wrote, or you listen to the preacher, who is simply giving you his opinion on the book, or his personal beliefs on the manner.
And then there's the fact that it's very arguably better and more virtuous to do something for it-self, and not for some other reward. As in, if you're only acting good because you think it'll lead to you Heaven, or something, then as soon as you think something will lead you to heaven, that becomes "good," no matter how wrong it arguably is. Again, look at all the atrocities commited in the name of Religion through out history.
My point isn't to demonize religion, it's that religion is completely irrelevant to morals and ethics. Morality and ethics are grounded in genetics and culture, something religion is only a part of.