After these words, G-d’s word came to Abram in a vision, saying, “Do not fear, Abram. I am a shield for you; your reward will be very great.”
Genesis 15:1
According to the logic of strict justice, finite acts of goodness should elicit a commensurately finite reward. G-d, however, bestows upon us infinite reward for our fulfillment of His commandments. This is the meaning of “Your reward shall be very great.”
The reason for this is because the Torah’s commandments are both finite and infinite. On the one hand, each commandment refines one particular aspect of our animal nature and is performed in a finite, physical way. On the other hand, each commandment also expresses the will of the infinite G-d, and thus, fulfilling any one commandment connects us with infinity.
We therefore receive both finite and infinite reward, corresponding to the two aforementioned aspects of the commandments.
--Daily Wisdom Vol. 3