Commentary for Leviticus 1:7

אש … ‎ונתנו AND [THE SONS OF AARON …] SHALL PUT FIRE [ON THE ALTAR] — Although the fire descended from heaven, it was nevertheless a religious duty to bring also some fire of profane origin (Sifra, Vayikra Dibbura d'Nedavah, Chapter 5 10; Yoma 21b; cf. Rashi on Leviticus 10:2 and Note thereon).

ונתנו בני אהרן, ”the sons of Aaron are to place the blood, etc.” The reason why the Torah uses the plural mode, -as if one priest by himself could not perform this task- is that it is customary for the Torah when describing the functions performed by the priests in the Tabernacle, to use the plural mode. There used to be numerous priests milling around in the Temple precincts, seeing that there they would be in the proximity of the Shechinah. We have the principle of ברוב עם הדרת מלך, when the king is surrounded by a multitude of his subjects this reflects positively on the degree of his glory.” [Menachot 62 (et al) where a function is distributed amongst 3 priests although a single one could easily have performed it by himself. Ed.]