613. Pots on Pots

Shabbos 4:6

A person is permitted to put a metal pot on top of another metal pot on Shabbos, as well as an earthenware pot on an earthenware pot, an earthenware pot on a metal pot, and a metal pot on an earthenware pot. One may seal either type of pot using dough since the intention is not that the pot should be heated more, just that the heat should be preserved. The Sages only prohibited covering pots with other things on Shabbos but one may place vessels on top of vessels in order to keep them hot. However, one may not place a vessel containing cold food on top of a hot vessel on Shabbos because this heats it. One may, however, put cold food on top of a hot pot before Shabbos. This is not the same as insulating food with something that raises its temperature.

Shabbos 5:1

Lighting a Sabbath lamp is not optional, nor is it a situational mitzvah such as washing hands, which one must only do if he chooses to eat bread. Rather, it is a full-blown obligation. Both men and women must have a light burning in their homes on Shabbos. Even one who does not have food to eat should beg door to door in order to buy oil for his Shabbos lights; this is considered part of the mitzvah of delighting in Shabbos. A bracha must be recited before lighting just as one does before fulfilling any of the rabbinic mitzvos. The bracha is that God “has sanctified us with His commandments and commanded us to kindle the Sabbath light.”