In my opinion, we usually don't do things just for one reason, there are a whole variety of reasons that affect our choices. Some of them are selfish reasons, some of them are not. The existence of selfish of reasons on its own is not a bad thing.
For example, when i help someone, aside from wanting to help him for his sake, i also feel better about myself as a human, which usually makes me happy. I feel happy for him, which in itself also serves me as obvious, as i'm happier regardless. Then there are the reasons related to consequences, obviously we all get affected by that in one way or another, which also in itself is not a bad thing.
Finally, for me there is another motive, which is pleasing what i perceive as my creator, fulfill his expectations (which is also partially self serving i guess, but not entirely). To make it clear though its not just for reward or to avoid punishment from that god, but for the sake of pleasing him in itself as well. Its difficult to separate all these motives, and trace which is the main motivator for you most of the time and in each situation.
So basically, this last part is just a different set of motives which people who believe in that kind of god have.