Комментарий к Дварим 22:7

למען ייטב לך וגו׳ THAT IT MAY BE WELL WITH THEE etc. — If in the case of an easy command which involves no monetary loss, Scripture states “Do this in order that it may be well with thee and thou mayest prolong thy days”, it follows à fortiori that this at least will be the grant of the reward for the fulfilment of commands which are more difficult to observe (Chullin 142a).

למען ייטב לך והארכת ימים, in the matter of dispatching the mother bird before taking her chicks, we find some display of protective concern by the Torah for the preservation of the species, an effort not to destroy the seed of the birds of the field although they are הפקר, unclaimed property. In the example of the dispatch of the mother bird the Torah appears to teach us that even the display by us of concern for such totally unclaimed eggs or chicks is rewarded by the Creator with the party showing this empathy receiving dividends in this life and the principal (reward) in the world to come.