According to the Sages, the above verse contains a metaphor. Not only did the Children of Israel not find water, but they did not find Torah either, which is compared to water. In other words, while they should have reached Mount Sinai within three days after having left the splitting of the sea, they did not. What happened?
The Midrash explains that their delayed journey was a repercussion — a result of selfishness. A literal reading of the verse states that Moses “travelled” the Children of Israel from the sea.
Based on this peculiar language, the Sages explained that Moses needed to force them away from the waters. This is because the people were determined to remain at the water’s edge to collect the Egyptian booty that was beginning to flow to the shores, instead of hurrying to Mount Sinai to receive the Torah.
As a result of this failing, instead of going directly to Mount Sinai, the people were first brought to Marah in order to prepare them for what was to come. As the verse states, “There [God] made for them a statue and a law, and there He tested them” (Exodus 15:25).
This episode may explain a teaching in Rambam. In his laws of Torah study he instructs, “No instructions in the Torah should be given to any but a fit student of proper conduct… but if one followed a way which is not good, we first must bring him back to goodness and lead him in the path of righteousness… after which we may admit him to the Bet Hamidrash and give him instructions” (Talmud Torah 4:1).
In other words, there are two components to being a Jew, the human and the religious. A Jew must first and foremost be a good person and above that aspire to be a good Jew. The Jewish people may have already left the depravity of Egypt but they showed that they weren’t ready yet to receive the Torah. Only once they worked on themselves were they ready to take that next holy step.