At the climax of the Tabernacle’s dedication ceremony, described in Parashat Shemini, fire descends from the heavens and kindles the wood arrangement on the bronze altar. Even though that fire burned perpetually, there is a commandment to add fire kindled by a person to it.

“The sons of Aaron the priest shall place fire upon the altar” (Leviticus 1:7). Even though the fire on the altar descends from the heavens, there is a commandment to place fire from an ordinary source. The fire that descended during the days of Moses did not leave the bronze altar where offerings were sacrificed until the Israelites arrived at [i.e., built] the eternal Temple. The fire that descended during the days of Solomon did not leave the altar of the burnt offering until it left hundreds of years later during the days of Menashe [a king from the house of David who sinned excessively]. (Sifra, Vayikra Dibbura diNedava 4)