“There (while the Jews were encamped at Marah), He (G-d) established for the nation a decree and an ordinance, and there He tested it” (Ex. Ch.15 V.25).
This portion takes place after an amazing string of events where the Jews had seen and experienced the hand of G-d. First they had seen the ten plagues performed by His emissaries Aron and Moshe. Then, after having been freed by Pharaoh, Pharaoh reneges and chases the Jews. While the Jews are standing between the water on one side, and the Egyptian army on the other, G-d miraculously splits the sea. But it was not just what G-d did, but how He did it. The Mechilta (Midrashic source) explains that the ground on the bottom of the sea turned solid so the Jews would be able to walk easier, and fresh fruits and spring water were literally coming out of the walls that the water had created (when the sea split, it split into twelve different compartments, one for each tribe). These extra “smaller” miracles indicated to the people the special concern G-d had for them.
Yet after seeing these amazing events, there was an inevitable letdown. A person can only gain a certain amount through visual stimulus. Visual events can provide a beginning, but something tangible must come into place in order to reinforce that which they have seen.
Now that the Jews had escaped their jailers, they were counting down forty nine days until the receiving of the Torah. In this time, they were meant to spiritually prepare themselves. In the meantime, however, G-d wanted to give them a few commandments to “hold them over” until the receiving of the Torah.
In the aforementioned verse it mentions a “decree” and an “ordinance”. This means that at Marah, G-d gave them a few commandments. The decree was the mitzva of Parah Adumah—the Red Heifer (the Red Heifer enabled the Jews to remove the spiritual taint of death). Amongst the ordinances was Shabbos.
Why was such a fundamental mitzva such as Shabbos, first given “quietly” with no specific mention, merely alluded to at Marah, before being given explicitly at Har Sinai as one of the Ten Commandments?
As a general rule, the way in which something is given sets the tone for how it is received.
In Judaism, a great premium is placed on the value of tznius—modesty: that things don’t always have to be broadcast from the roof. Very often, the more things are exposed to the public, the more cynical people become about them. Everything seems to be known about them, thus removing from their uniqueness. Sadly, we live in a society which places a tremendous premium on external values – where if something is not done with pomp and circumstance, it’s almost as if it didn’t happen. These ideas are antithetical to Judaism. (Incidentally, this is the mistake of some people who wrongly decide that traditional Judaism is anti-woman, as opposed to understanding that there are external and internal roles. We will, G-d willing, discuss this more in depth another week.)
To set this tone, G-d initially gave the mitzva of Shabbos in relative privacy, at Marah (of course the process at Har Sinai was also necessary, so the Jews could hear from G-d first hand). It was meant to be a lesson for the ages, to see the internal value as opposed to the external one.