Musar zu Schemot 5:3

Onkelos translates the words "the G–d of the Hebrews has called upon us," as "the G–d of the Hebrews has revealed Himself to us" (Exodus 5,3). What he means by this is that a new perspective of the universe had been revealed for the sake of Israel. From now on Israel would be the fruit and everything in the universe would become of secondary importance. The reason Israel would become of primary importance was that they would travel three days' distance into the desert, to receive the Torah. This is in accordance with the statement in Baba Kama 82, that the verse "they walked three days in the desert and did not find water," refers to their not receiving the Torah during that period (Exodus 15,22). We have a tradition that אין מים אלא תורה that the true meaning of "water" is Torah (Baba Kama 17). Their fatigue was due to the absence of Torah, which would have inspired them. Isaiah 55,1, refers to this מים-תורה according to the Talmudic source quoted. It was then that the prophets arranged for public Torah readings on every Sabbath, Monday and Thursday, to insure that Israel would never be without the benefit of Torah for three days.