If you will heed these ordinances, and safeguard them, and perform them, G-d, your G-d, will keep the covenant for you, as well as the promise of kindness that He swore to your forefathers.
The reward for performing the commandments cannot be only material blessing and plenty, since such a reward would not be commensurate with the far-reaching effects of fulfilling the commandments. The sages point out that even the immeasurable delight experienced by the soul in the afterlife is insufficient compensation for even one hour of performing G-d's will in this world.
Rather, the intimacy with G-d that we achieve by fulfilling His commandments is their true reward. Hence, the material bounty promised in the Torah is not an end in itself but rather simply the means by which G-d facilitates our further performance of His commandments.
Similarly, the material bounty awaiting us in the Messianic era is not an end in itself but the circumstance that will enable us to fulfill G-d's will and perform the commandments in the most ideal way possible.
From Kehot's Chumash