Musar for Shabbat 139:13

Our sages also add to that an additional rule: We learn from the singling out of a particular work-prohibition that if a person violates more than one of the 39 work-prohibitions on the Sabbath he is liable for a separate penalty for each one of such transgressions. The Yerusalem Talmud Sanhedrin 4,6 derives from the words "in all your dwellings," that no Court is to sit on the Sabbath.

When G–d began the work of Creation, He said: "Let there be light," the foundation of fire. There is both visible and hidden fire. This is the mystical dimension of the Torah's commandment in Exodus 35,3: לא תבערו אש בכל מושבותיכם ביום השבת. "Do not light a fire in any of your dwellings on the Sabbath day." The Torah singled out this prohibition of work (whereas none of the other 38 basic prohibitions of work is named).