A lot of that depends on what constitutes 'serving' god. Like, if god suddenly appeared and asked me to kill my first born son to get into heaven, I'm going to say no. If he asks me something reasonable, like volunteer at a soup kitchen, then I'd be more than happy to help out. I have my own moral code without a god, and I'm not about to change it just because he told me to. Besides, if god told me to do something I didn't agree with, how do I know the heaven he is offering is one I want to be in? I don't want to go to a place with a whole bunch of child murderers who listened to god.