After the grievous sin of the golden calf, the Children of Israel seek a way to return to Hashem. Moshe brought down the second Luchot on Yom Kippur (the 10th of Tishrei), indicating that they were fully pardoned, but the people want more. They want every trace of their sin removed, their original relationship with Hashem restored.
The Mishkan was intended for this purpose of kapparah (atonement). Through building the Mishkan the people would achieve the return to Hashem they yearn for.
However, before beginning his instructions regarding the construction of the Mishkan, Moshe teaches the people the importance of Shabbat: And Moshe assembled the entire community of the Children of Israel, and he said to them, "These are the things that Hashem has commanded to do them: For six days shall work be done, and the seventh day shall be holy for you, a complete Shabbat rest for Hashem; anyone who does work on it shall be put to death. You shall not kindle (T'VA'ARU) fire in all of your dwellings (MOSHVOTEICHEM) on the Shabbat day" (Shemot 35:1-3).
Here, Moshe repeats Hashem's original instructions about observing Shabbat as stated in 31:12-17. The crucial work of the Mishkan will continue ceaselessly all week, yet it will be halted for Shabbat.
What is the meaning of specifying the Shabbat prohibition of: You shall not kindle fire in all of your dwellings on the Shabbat day.
A number of answers are found in the sources, including:
However, the connection between the verse and the mitzvah-derivation seems remote, and requires explanation.
Haketav V'hakabbalah (R. Yaakov Tzvi Mecklenburg, 1785-1865) gives a detailed analysis of this verse, including a scientific explanation of the workings of fire, as well as some complex Talmudic issues. His main points are:
R. Mecklenburg concludes with a declaration of the stringency of Shabbat: Although offering the sacrifices and operating the Sanctuary will prevail over the laws of Shabbat, its holiness is not overridden, neither by the building of the Mishkan nor by punishing the guilty. It is often said that building a "sanctuary-in-time" (Shabbat) is a higher priority than building a "sanctuary-in-space" (Mishkan). But, what of punishment, which is the duty of the court and brings atonement to the life of the criminal (Tosafot to Sanhedrin 35a)? Why does Shabbat supersede punishment? Sefer Ha Chinnuch (ascribed to either R. Aharon HaLevi or R. Pinchas HaLevi of Barcelona, mid-13th Century) provides us with an analogy: A great king summoned the people of the country one day to a feast, when he would not withhold entry from anyone, and after the day of the feast he would sit in judgment. Shabbat is a day's reprieve for all, a day without guilt or judgment, worry or punishment. On this day we are all equally the guests at the King's table, for it is a day for us to find the forgiveness we seek.