And the 29th mitzvah is that we are commanded to burn a constant fire on the altar each day.

The source of this commandment is G‑d's statement,1 "Fire shall be kept burning on the altar continually; it must not go out." This is impossible2 without a command to constantly place wood [on the fire] each morning and evening, as explained in the 2nd chapter of tractate Yoma3 and in tractate Tamid.4

Our Sages said explicitly,5 "Even though the fire came down from the heavens, it is a commandment for mortals to bring it."

The details of this commandment, i.e. of arranging the fires on the altar each day, have been explained in the 4th chapter of tractate Kippurim6 and in the 2nd chapter of tractate Tamid.