Charles Ellicott Commentary 1 Chronicles 23:31

"and to offer all burnt-offerings unto Jehovah, on the sabbaths, on the new moons, and on the set feasts, in number according to the ordinance concerning them, continually before Jehovah;" — 1 Chronicles 23:31 (ASV)

And to offer all burnt sacrifices. —Rather, And over all offering of burnt offerings. The Levites had to select and prepare the victims; the priests offered them, when ready, upon the altar. The Levites had to do this “by number,” i.e., according to the several numbers prescribed by the Law for each occasion (see Numbers 28).

According to the order commanded to them. — According to the rule concerning them: i.e., concerning the sacrifices.

Continually. —Heb., tamîd, the technical term in connection with the burnt offerings, which regularly recurred at stated times, e.g., a lamb was offered morning and evening .