Musar על קידושין 78:6

4) A fourth level of מצוה performance is performance of the commandment for the sake of G–d, not for the securing of any kind of advantage on this earth. Abraham was a prime example of this when he risked his life to liberate Lot and incidentally all the people of Sodom, etc, and refused as much as a shoelace of the loot which was legally his (Genesis 14,22).

The laws pertaining to paying the hired laborer on time, the rules about what the laborer may consume when engaged in harvesting the owner's field, etc., are all allusions to our relationship to G–d our "employer." It is incumbent upon us to be His loyal servants; if we are, the Torah promises us and we expect to receive recompense in the form of enjoyment of "dividends" such as eating while working in the fields of this world. The "principal," the main reward for the מצות, is in the Hereafter: this clearly implies that we must not expect to take home in this world any of the fruit we harvested [in the field]. Basically, reward for commandments performed is not collected in this world. This is alluded to by the prohibition to eat any of the fruit of the field or orchard still attached to the ground (23,26).