A shabbat Table
A shabbat TableMendi Hochsman/Flash 90

We were first introduced to Shabbat at the end of the Torah's account of Creation. We next encountered it in the Torah's account of the MAHN (manna) that HaShem gave the people a month or so out of Egypt. In that context, we are taught the mitzva of T'chum Shabbat, the Shabbat boundary.

It was in last week's sedra that we are commanded both the positive mitzva of sanctifying Shabbat as it enters (Kiddush, in davening and with wine) and as it exits (with Havdala, in davening and with wine, spices, and candle).

And, in the same parsha (Commandment #4), we find the few words which are attached to a mountain of halachic detail (ref. Mishna Chagiga 1:8) of the prohibitions of Melacha on Shabbat. LO TAASEH KOL M'LACHA...

So far, the Shabbat seems to be a huge set of Don't do that and don't do this, and a relatively small positive component of ZACHOR.

Until we get to mid-Mishpatim (actually, at the 2/3 mark). There we find 23:12 - ...and on the seventh day you shall rest...

This is NOT the source of taking a nap on Shabbat. That we learn from the pasuk in Yeshayahu (58:13) declaring the Shabbat as ONEG, a day of delight.

What we learn from the pasuk in Mishpatim is the mitzvat asei, the positive command to abstain from melacha.

Don't cook and abstain from cooking sound the same. Don't write and abstain from writing sound the same. 37 et ceteras. Actually, Don't sew is straightforward. Abstain from sewing (or sowing - they are both melachot) seems an awkward way to say the same thing. But there is a significant difference - not just linguistic.

One of the differences between an ASEI and a LO TAASEI which of two sides of the same coin, is that not violating a prohibition is generally motivated by YIR'AT HASHEM, fear of G-d. I won't do that because He told me not to. There is also fear of punishment.

Observing an ASEI is becoming partners with HaShem and doing as He asks because of AHAVAT HASHEM. See Sedra Summary, middle of Chamishi for more - especially, Dayan Grunfeld's approach.
We find a similar set of mitzvot with Sh'mita. In Parshat B'har, there are several prohibitions concerning the Sabbatical year. Don't do this and don't do that.

But in Mishpatim (the pasuk right before the Shabbat one we have been discussing), we find And on the seventh year you shall leave (your fields) unattended and unharvested...
Prohibitions are set down in a stern manner, including (sometimes) details of the harsh punishments that come from violation.

In the positive presentations of these same mitzvot, we can feel G-d's arm, so to speak, around our shoulders, and His asking us to DO such and such, because we are His people and He wants us to derive positive lessons from our observance, and appreciation for Him.