“Hashem Elokecha Imach Lo Chasarta Davar; Hashem was with you in the Midbar and you lacked nothing (Devarim 2:7).” The Imrei Yitzchok asks that the beginning of the pasuk already said this in different words, why does the second half of the pasuk repeat it?
He answers that there is a mitzva to pay a worker on the day he completes the job, and it is an aveira to delay. If so, how is it that “Schar Mitzva B’Hai Alma Leka; Hashem does not reward us for doing mitzvos in this world,” when He has a Chiyuv to pay immediately? The answer is that the halacha is if you hire someone through a Shaliach, and not personally, then the issur does not apply. Therefore, Hashem who gave the mitzvos through Moshe Rabbeinu is not obligated to pay right away, and instead he saves it for our benefit in Olam HaBa.
This applies to only 611 mitzvos. However the Mitzva of Emuna which Hashem said himself on Har Sinai when He said, “Anochi Hashem Elokecha,” and, “Lo Yihiyeh,” does require immediate payment. In this world we live off the schar of our emunah.
The beginning of the pasuk tells us that Hashem sustained us in the Midbar. The end of the pasuk explains why. “Hashem Elokecha Imach” because we had emuna in Hashem. Therefore, he needed to pay us and, “Lo Chasarta Davar.”
From Revach.net