We are not on the same page

I am a person who has faith and who strongly believes in God. When I was in high-school at Religion class one of my colleagues asked the teacher if we do a good thing, should we expect a reward or should we do something good without expecting to be recognized for it?  The answer my teacher gave was unexpected. She said that it’s not wrong to wait for a reward, it’s not selfish. I felt that that wasn’t the best thing she ever told us, because we can’t always expect  rewards and prizes for everything we do. We don’t need to help someone only because we believe that we will be rewarded. I didn’t agree with my teacher that day, and I wish I told her my honest opinion, but I didn’t say anything. I regret it.