Although the manner in which the Torah expresses the Mitzvah of Shabbat in the Aseret HaDibrot in Parashat Yitro differs from the portrayal in Parashat VaEtchanan, Chazal teach that “Zachor VeShamor BeDibbur Echad Ne’emru,” “Zachor and Shamor were commanded by Hashem simultaneously.” What still remains a question, however, is why Hashem chose to write Zachor in Parashat Yitro and Shamor in Parashat VaEtchanan.
The Meshech Chochmah explains that the practices of the Torah can be divided into two categories: Mitzvot Aseih and Mitzvot Lo Taaseh, and thoughts and deeds. For example, faith in Hashem is a positive commandant of the first category, while understanding the vanity of idol worship is fulfilling a negative commandment of thought. Wearing Tefillin and reciting Kiddush on Shabbat are positive commandments of the second category, while avoiding forbidden foods and avoiding Melachah on Shabbat are negative commandments of the second category.
The Meshech Chochmah asserts that the positive Mitzvah of “thought” is much more difficult to fulfill than the negative Mitzvah, yet the positive Mitzvah of “deeds” is easier to perform than its negative counterpart. For example, it is not a difficult task to believe that idols have no power and no authority, but it is a much more difficult task to believe constantly that Hashem is aware of what is happening to each individual at all times and that everything happens solely as an effect of His will.
On the other hand, it is much easier to put on Tefillin every day than to constantly avoid the temptation of eating forbidden foods or engaging in Melachah on Shabbat.
It is precisely because of this reasoning that the Torah writes Zachor in Parashat Yitro. At this exact time, the Jews began their journey in the Midbar, within which creating a sense of sanctity on Shabbat without a real home and community actually was more difficult than avoiding Melachah. No one had any desire to plant or harvest, because the Mann fell daily, and most of their daily needs were provided by Hashem without any effort on the collective part of Bnei Yisrael. Thus, Hashem commands Bnei Yisrael “Zachor Et Yom HaShabbat LeKadesho” (Shemot 20:8), make Shabbat a special time.
However, in Parashat VaEtchanan, when Bnei Yisrael are about to enter Eretz Yisrael, where much more physical labor and involvement occurred during the nation’s daily functioning, Hashem commands Shamor, the emphasis being placed upon the more difficult aspect of Shabbat, refraining from violating one of the 39 Melachot.
Although at the time the Torah was written certain criteria were expected of Bnei Yisrael at different intervals, we enjoy the luxury of having received the Torah in its entirety and, as a result, we are aware of all of its various limitations and requirements. It therefore is our duty to be fully conscious of what Hashem and the Torah are asking of us and to fulfill every facet of the Torah’s commandments to the best of our ability.