Two Forms Of Shabbos

Why does the issur of kindling a fire on Shabbos appear in this week's parsha?  

The meforshim ask why does the mitzvah of mishkan in Ki Sesa precede that of Shabbos to tell us that Shabbos doesn't override the mishkan but in Vayakhal it is reversed?  Many distinguish between before the chait haegel and afterward in different variations.  Rav Tzaddok (Vayakhal #8) explains that there are two forms of Shabbos.  One form is that Shabbos comes to elevate the days that preceded it and the other is that Shabbos comes to cap off the week with an added layer of kedusha.  This is reflected in the machlokes in the Gemorah Shabbat (69b) if one who is lost in the wilderness and doesn't know the day works six days and keeps the last day as Shabbos or keeps the first day as Shabbos and works the rest.  The debate is if Shabbos precedes or caps off the week  The original plan for Shabbos was for Adam to pass his test on Friday and enter a sublime realm of kedusha where Shabbos comes to add to that kedusha and cap off the week.  After Adam stumbled, Shabbos was necessary to uplift the upcoming days which were now mangled and marred by sin. Similarly, before the agel, in Ki Sesa, the Shabbos was the end of the week version.  It wasn't coming to fix anything but was a infusion of kedusha as a culmination of the week.  Mishkan comes first and Shabbos adds a layer of kedusha to the ever present kedusha.  After the agel, when sin again tainted the daily activities, Shabbos was necessary to allow one to bring kedusha into the days ahead.  First comes Shabbos and only afterward comes the mishkan. 

The Rebbe (Likutay Sichoos volume 36) asks why does the Rambam (Ch, 12) of Shabbos starts the melacha of fire with the case when the ashes are needed and not with the simple case of a fire for light or warmth?  After explaining the nigla, he says בפנימיות this alludes to the fact that the fire of the neshama which wishes to join with Hashem as described in Tanya Ch. 19 must be rooted in צריך לעפר, it has to illuminate the physical world.  This may be why the melacha of fire is introduced in this parsha because it illuminates the essence of Shabbos post agel.  Shabbos it here to give light, to add kedusha to our mundain days.