Immediately after the miraculous Keriat Yam Suf and Bnei Yisrael’s subsequent praise of Hashem with Shirat HaYam, Bnei Yisrael are confronted with their first non-Egyptian challenge: the waters at Marah are too bitter for them to drink. This seemingly basic problem turns into an entire lesson in Emunah that Hashem imparts to Bnei Yisrael. It is not sufficient for Him to simply sweeten the water and make it drinkable, but “Sham Sam Lo Chok UMishpat VeSham Nisahu” (15:25) – Bnei Yisrael are also given certain Chukim and Mishpatim to follow. On top of that, the incident finishes with what seems to be a promise from Hashem that if Bnei Yisrael follow the Mitzvot, which they will soon receive, then Hashem will not inflict them with the diseases that He used to punish Mitzrayim. What is it that Bnei Yisrael lack that causes this incident, and how does the institution of these specific laws correct the problem?
Ramban explains that now, prior to entering the desert, Bnei Yisrael are given Chukei HaMidbar, rules regarding how to deal with the hardships of the desert. When there is no water, instead of complaining as they do here, they should pray to Hashem to help them. Additionally, they are given Mishpatim that deal with how to live their everyday lives. These include loving other people, following the words of the Zekeinim, Hilchot Tzniut that pertain to women and children, and other laws regarding how to act within the camp. At this point, Bnei Yisrael still suffer from a slave mentality, a syndrome which will linger until they enter Eretz Yisrael. A slave focuses on his individual, physical needs and seldom thinks of how to act spiritually or relate to other people. Therefore, Am Yisrael is given guidelines that help rectify its deficiencies in these areas. Additionally, Bnei Yisrael have no experience as a free nation and must be instructed how to act on a national level.
This idea also explains the reason for the Marah incident. The issue at hand is not the bitterness of the water, but rather that Bnei Yisrael do not know the proper solution to the problem. Instead of complaining to Moshe, they should take the initiative and pray to Hashem for help. However, because complaining is the only response to difficulty that they have known until this point due to their slave mentality, they have to be taught the proper way to resolvesuch a situation.
Alternatively, Rashi states that the phrase “Sham Sam Lo Chok UMishpat VeSham Nisahu” refers to the Parshiyot of Shabbat, Parah Adumah, and Dinim, which are given to Bnei Yisrael after the Marah incident to discuss. The Gur Aryeh explains, based on Sanhedrin 56b, that Dinim refers to Dinei Mamonot, monetary laws, which must be judged by a Beit Din and are hinted to by the word “Mishpat” in the Pasuk. On a practical level, it is understandable that this sphere of Torah be presented at this point. Having just formed a nation, Bnei Yisrael will need to know how to deal with such issues, and more importantly, how to apply Halacha to the situation at hand. Additionally, it makes sense that these are given to Bnei Yisrael specifically at Marah, as it is their inability to solve problems and apply knowledge that causes them to complain rather than take initiative.
With regard to Parah Adumah and Shabbat, on the other hand, a different element is involved. Rav Yaakov Kamenetzky explains in his Sefer Emet LeYaakov that the miracle of water turning sweet when wood is thrown into it (as the waters of Marah did) shows that all Parnasah depends on the will of Hakadosh Baruch Hu. Only once this lesson is taught is it possible to command Bnei Yisrael to keep Shabbat, whose main challenge is that it prevents a person from working to acquire the necessities of life. Shabbat tests our ability to recognize that everything is really in the hands of Hashem.
Rav Yaakov goes on to quote the Midrash in Shemot Rabbah (5:18) which states that the main source for Bnei Yisrael’s Bitachon during Galut Mitzrayim was their reading on Shabbat of Megillot describing the future Geulah. However, during the final year of slavery, Pharaoh decreed that Bnei Yisrael stop reading these Megillot and begin working on Shabbat. (This is hinted to by 5:9, where Pharaoh says, “Tichbad HaAvodah Al HaAnashim VeYaasu Vah, VeAl Yish’u BeDivrei Shaker.”) Therefore, just like the source for Bnei Yisrael’s Bitachon in Mitzrayim was Shabbat, so too their source for Bitachon once they leave Mitzrayim will be Shabbat. Thus, it is Bnei Yisrael’s lack of Bitachon that causes them to complain, and it is Shabbat that will instill them with Emunah once again.
Nonetheless, the reason for teaching Parah Adumah here seems much more obscure. What is the need for a Mitzvah that has no application now, before Matan Torah? Rav Yaakov notes that the main purpose of these laws is for Bnei Yisrael to discuss Torah, as Rashi explains. They are not necessarily practicing these Mitzvot just yet, but rather learning the Sugyot as preparation for Matan Torah. There is no greater preparation than learning the Sugya of Parah Adumah, which man cannot fully comprehend; only Hashem can understand the logic behind an item that can simultaneously purify the impure and contaminate the spiritually pure. Such a concept would teach Am Yisrael before Matan Torah that Torah lies beyond the simple understanding of a person, but rather is much deeper than anything else in the world.
Similarly, the Torah Temimah points out a comment of the Gemara in Bava Kama 82a based on the idea that “Ein Mayim Ela Torah,” that water is often a symbolic reference to Torah. The Gemara infers from the introductory Pasuk to the Marah story – “…Vayeilchu Sheloshet Yamim BaMidbar VeLo Matz’u Mayim” (15:22) – that the Neviim established Torah reading on Mondays and Thursdays to prevent one from going three days without learning. It is thus clear that one of the causes for this incident was the lack of Torah amongst Bnei Yisrael. “Deracheha Darchei Noam,” the ways of the Torah are peaceful, but the converse is also true – when there is no Torah, there is no peace. The use of an Eitz, a piece of wood, to cure the problem hints that Torah was the real remedy, as Torah is also compared to an Eitz (“Eitz Chayim Hi LiMachazikim Bah”). The giving of the first few Mitzvot after Marah thus prepared Bnei Yisrael for Matan Torah.