John Gill Commentary 1 Kings 18:39

"And when all the people saw it, they fell on their faces: and they said, Jehovah, he is God; Jehovah, he is God." — 1 Kings 18:39 (ASV)

And when all the people saw it, they fell on their faces
In reverence of God, astonished at the miracle wrought, ashamed of themselves and their sins, particularly their idolatry, that they should turn their backs on the true God, and follow idols:

and they said, the Lord, he is the God, the Lord, he is the God;
which acknowledgment of God, as the true God, in opposition to Baal, is repeated, to show their firm belief and strong assurance of it.