Observing a commandment because of reward and punishment or observing a commandment for its own sake?

Hello Rabbi
I read the trilogy that says that keeping the commandments is important to you for its own sake and not for any other purpose. I wanted to ask, how does this fit in with the concept of a reward system, how do you understand the High Holy Days (what we pray for), since you don’t keep the commandments because of the reward and punishment system?