Albert Barnes 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)

The Lord, he is the God - The people thus declared the matter to be clearly and certainly decided. Baal was overthrown; he was proved to be no god at all. The Lord Yahweh, He, and He alone, is God. From that time forward, they would acknowledge Him and no other.