Albert Barnes Commentary Leviticus 9:24

"And there came forth fire from before Jehovah, and consumed upon the altar the burnt-offering and the fat: and when all the people saw it, they shouted, and fell on their faces." — Leviticus 9:24 (ASV)

The very ancient Jewish tradition has been widely adopted that the sacred fire of the altar originated in this divine act, and that it was afterward preserved on the altar of the tabernacle until the dedication of the temple, when fire again came down from heaven (2 Chronicles 7:1).

But according to the sacred narrative, the altar-fire had been lit in a natural way before this occasion. (Leviticus 9:10; Leviticus 9:13, and other similar passages; Exodus 40:29.) It would therefore seem that the fire which came out from before the Lord manifested itself, according to the words of Leviticus 9:24, not in kindling the fuel on the altar, but in the sudden consuming of the victim.

For similar testimony to the acceptance of a sacrifice, see Judges 13:19-20; 1 Kings 18:38; 1 Chronicles 21:26; and probably Genesis 4:4. The phrase to turn a sacrifice to ashes became equivalent to accepting it (Psalms 20:3, see the margin).

The fire of the altar was maintained in accordance with Leviticus 6:13.