Rain, corn, wine and oil, grass for the cattle the catalogue of rewards is endless. But is that the reason why we decide to obey the commandments? Are we spurred on by the thought of reward, or do we do the right thing for its own sake?
One answer is that the righteous need no reward. They act lishmah, doing the right thing because it is right. They probably prefer that rewards should not exist so that they never feel tempted to act for an ulterior motive. For them the reward is at best a consequence but not the motive of a mitzvah.
That’s all right for the tzaddikim, but most people are not (yet) on that level. For the ordinary person the thought of a reward is useful. If they will only act when there is talk of a reward, then let the reward be there as an encouragement. Better a mitzvah with a reward than no mitzvah at all.
Nonetheless this is not the highest ethic. We hope the thought of a reward will train people so well to do mitzvot that the time will come when the possibility of a reward will become quite unnecessary. That’s when we will be able to say with Pir’kei Avot (4:2), s’char mitzvah mitzvah, “the reward of a mitzvah is the mitzvah“.