And there came a fire out from before the LORD, and consumed upon the altar the burnt offering and the fat: which when all the people saw, they shouted, and fell on their faces.

Wesley's Notes

9:24 And there came a fire - In token of God's approbation of the priesthood now instituted, and the sacrifices offered, and consequently of others of the like nature. And this fire now given was to be carefully kept, and not suffered to go out, Lev 6:13, and therefore was carried in a peculiar vessel in their journeys in the wilderness. From before the Lord - Or, from the presence of the Lord, that is, from the place where God was in a special manner present, either from heaven or from the holy of holies. They shouted - As wondering at, rejoicing in, and blessing God for this gracious discovery of himself, and his favour. This also was a figure of good things to come. Thus the Spirit descended in fire upon the apostles, so ratifying their commission, as this does that of the priests. And the descent of this holy fire into our souls, to kindle in them devout affections, and such an holy zeal as burns up all unholiness, is a certain token of God's gracious acceptance.

Jamieson-Fausset-Brown Bible Commentary

24. there came a fire out from . the Lord-A flame emanating from that resplendent light that filled the holy place flashed upon the brazen altar and kindled the sacrifices. This miraculous fire-for the descent of which the people had probably been prepared, and which the priests were enjoined never to let go out (Le 6:13)-was a sign, not only of the acceptance of the offerings and of the establishment of Aaron's authority, but of God's actual residence in that chosen dwelling-place. The moment the solemn though welcome spectacle was seen, a simultaneous shout of joy and gratitude burst from the assembled congregation, and in the attitude of profoundest reverence they worshipped "a present Deity."

Matthew Henry's Concise Commentary

9:22-24 When the solemnity was finished, and the blessing pronounced, God testified his acceptance. There came a fire out from before the Lord, and consumed the sacrifice. This fire might justly have fastened upon the people, and have consumed them for their sins; but its consuming the sacrifice signified God's acceptance of it, as an atonement for the sinner. This also was a figure of good things to come. The Spirit descended upon the apostles in fire. And the descent of this holy fire into our souls, to kindle in them pious and devout affections toward God, and such a holy zeal as burns up the flesh and the lusts of it, is a certain token of God's gracious acceptance of our persons and performances. Nothing goes to God, but what comes from him. We must have grace, that holy fire, from the God of grace, else we cannot serve him acceptably, Heb 12:28. The people were affected with this discovery of God's glory and grace. They received it with the highest joy; triumphing in the assurance given them that they had God nigh unto them. And with the lowest reverence; humbly adoring the majesty of that God, who vouchsafed thus to manifest himself to them. That is a sinful fear of God, which drives us from him; a gracious fear makes us bow before him.