These two mitsvot are obviously related, and fairly well known, so we will spend most of our space on aspects of these mitsvot that might not be widely understood. The basic obligation for the first is to positively command us to desist from those activities prohibited as melakhot on Shabbat, and for the second is to articulate verbally that Shabbat has arrived. (Doing so on wine or bread is generally seen as a rabbinic requirement).

Most simply, the first obligation delineates exactly the same religious experience as the prohibition of creative labor on Shabbat. Indeed, when the Sefer haHinukh discusses it in Mitsvah 85, he only says that he has already discussed it in the earlier Mitsvah prohibiting such activity (32). This view of the `aseh would also explain why we are sure that women are obligated (despite its being time-related). As we have mentioned before, however, Rambam seems to count the aseh's of a mitsvah separately from the lo ta`aseh because he sees them as having added religious content. Even Ramban, who generally sees the Torah's decision to make a mitsvah into an aseh and a lo ta`aseh as adding only to the severity of the commandment rather than to its religious content, here agrees with Rambam. These two authorities seem to agree that the `aseh is fundamentally the same, because they too apply it to women.

At the same time, they also use the `aseh to expand the scope of rest dramatically. Ramban notes that the Torah's prohibition against creative labor left open the possibility of nonetheless spending the day of Shabbat (and Yom Tov, for that matter) in heavy labor-- moving furniture back and forth is one still-relevant example. To avoid that possibility, Hashem also commanded us positively to rest on Shabbat. In his derashah le-Rosh haShanah, Ramban defines the word shabbaton as obligating rest in the simple sense of the term, in addition to the avoiding of creative labor made incumbent by the prohibitions of those days. Rambam opens the 21st chapter of Hilkhot Shabbat by mentioning that the word tishbot requires that we rest even from activities that are not specifically a melakhah. He then spends the next several chapters listing shvutin, rabbinically prohibited actions, many of them included because they are similar to melakhot de-oraita. While we might fool ourselves into thinking that Rambam is just adding a literary flourish with his introduction, it seems more likely that he is explaining the source of Hazal's decision to create so many shvutin— the verse tells us to avoid activities that smack of creative labor, not just that technically qualify as such labor.

To use an example recently pointed out to me, Rambam (following an explicit Talmudic statement) prohibits women from coloring their faces on Shabbat, as an extension of the melakhah of tsove`a, of painting or dying animal hides. Placing this in the context of tsove`a does not mean, as we might at first think, that we worry that someone who applies makeup or lipstick will then go out and do the same on a de-oraita level. Rather, Hazal saw the Torah's category as a paradigm for a type of activity in which we should not engage on Shabbat, and defined other similar ones.

Rambam's introduction to the chapter, then, is showing us that all of these rabbinic requirements actually have their root in a very general positive Torah requirement. Indeed, it also tells us that the Torah's list of 39 melakhot are not only the specific examples we can draw from the building of the Mishkan, they are meant as broad categories of activity from which we should desist on Shabbat. The act of building the Mishkan, then, encompassed the general types of creativity that would constitute a violation of Shabbat; by avoiding those, or others reasonably similar to them, we can fulfill Shabbat most completely.

In terms of the obligation of verbally declaring it Shabbat, the most obvious issue in Rambam's presentation is his inclusion of havdallah as a de-oraita obligation, based in the same verse of zakhor et yom haShabbat le-kadesho. Rambam's view seems to be based in his textual version of Pesahim 106a, where he apparently had the words bi-kenisato u-ve-yetsiato, when Shabbat enters and ends. Our texts just read bi-kenisato, which makes sense in context, since the gemara is discussing whether or not one must make kiddush during the daytime as well. Aside from the question of girsa, textual version, Rambam's view also radically changes the mitsvah. While our observance means that the Torah cared only about declaring Shabbat as it entered, Rambam's views the mitsvah as separating Shabbat from the rest of the week verbally. To do so, we must delineate both its beginning and its end ourselves.

In that version, the Torah might have cared about us "creating" Shabbat-- although the parameters of when we can do that are set by the sun and stars (before the stars come out on Friday, afterwards on Shabbat afternoon), the actual start and end of Shabbat is supposed to be done by us. Just as God's final creative act during the week was the creation of Shabbat, we are weekly enjoined (in Rambam's reading) to similarly create the day of rest.

Rambam's view of havdallah as a de-oraita obligation also has implications for women. Despite kiddush being a mitsvat `aseh she-hazman grama, Berakhot 20b derives an obligation from a comparison between zakhor and shamor (another indication that the positive and prohibitive elements of Shabbat observance are intertwined). For Rambam, that means that women are also obligated, on a Torah level, in saying havdallah at the end of Shabbat. Shabbat Shalom.