Halakhah for Shabbat 98:19

At the beginning of Parashat Vayakhel (Exodus 35:1) it is written, "And Moshe gathered etc. these are the things that the Lord commanded you to do: six days you shall do your melakhah and the seventh day should be holy to you etc." And the explanation is that God commanded them concerning the construction of the Mishkan and on Shabbat it was forbidden to do any of the constructive labors for the mishkan as is explained in the Midrash Mechilta. And from here we learn the tradition of the Sages to learn the general principles and great ideas of the labors of Shabbat. for from the juxtaposition of the matter of Shabbat and the construction of the Mishkan we learn that the forbidden labors of Shabbat were labors done in constructing the Mishkan. And so our Sages taught (Shabbat 49b): One is not liable other than for performing a labor of a variety that was done in the Mishkan. They sowed, you shall not sow. And sowing was done for the mishkan in order to plant ingredients needed for fabric dyes (according to Rashi). They reaped, you shall not reap etc. And from here we learned the 39 central categories of labor that were important for the mishkan (see the beginning of Bava Kama). and even though some of the melakhot are similar to each other such as winnowing, sorting, and sifting, for all of them are the removal of food from waste but the separating is done differently. Winnowing is by means of the wind and sorting is by hand and sifting is with a sieve. Nonetheless, since they were all distinct and important tasks in the Mishkan, they are all called Avot Melakhot (primal paradigmatic categories), and the other forms of labor that are comparable to the paradigms are called derivatives (toladot). (See Shabbat 73b).