The Mishna on today’s daf enumerates the 39 primary categories of labor that are prohibited on. These categories of labor are grouped according to their function, the first of which is the production of food (beginning with planting and harvesting through baking), the next preparation of clothing (beginning with shearing wool through sewing) and so forth.
The Gemara explains that the source for these specific categories of labor is derived from important activities that were performed in the Mishkan since the passage in the Torah that prohibits labor on is juxtaposed with the building of the Mishkan (see Shemot Chapters 31 and 35).
According to the explanation in Rashi and Tosafot, when the Sages speak of the labors performed in the Tabernacle as the source of laws, they are referring only to those labors involved in the construction of the Tabernacle. Therefore, they explain that the labors of plowing and sowing were necessary to grow herbs for producing dyes required in the Tabernacle. However, according to Rabbeinu Hananel and Rav Hai Ga’on, the relevant actions performed in the Tabernacle include those performed in preparing the sacrifices required in the dedication of the Tabernacle, e.g., plowing and sowing to grow wheat and barley for meal-offerings (Eglei Tal).
The primary categories of labor enumerated in the Mishna are a list of actions categorized according to certain criteria, as will be explained; however, the names of the labors do not express their essential nature. Consequently, it was necessary to add a list of subcategories that clarify the full range of actions prohibited under the rubric of each labor. In the Jerusalem Talmud, it is related that Rabbi Yoḥanan and Reish Lakish studied this chapter for three and a half years and found thirty-nine subcategories for each primary category of labor listed in the Mishna.