Quoting Commentary for I Kings 18:24

The seventh question: We see that the sanctification of the Sanctuary and Altar was effected by the descent of fire from Heaven upon the Altar, which consumed the offerings. The people saw and shouted and fell on their faces (cf. Leviticus 9:24). A similar passage appears in connection with Solomon's Temple: "When Solomon finished praying, fire descended from heaven and consumed the burnt offering and the sacrifices... All the Israelites witnessed the descent of the fire and the glory of the Lord on the House; they knelt with their faces to the ground and prostrated themselves, praising the Lord, 'For He is good, for His steadfast love is eternal.'" (2 Chronicles 7:1-3). So in the days of Elijah the sanctification of God was effected by fire: "...the god who responds with fire, that one is God." (1 Kings 18:24). Therefore, it is appropriate to ask, why was the divine sanctification effected by fire and not by water or something else?

On Har HaCarmel, Eliyahu HaNavi challenges the Nevi’ei Ha’Ba’al to prove the authenticity of their god. Eliyahu HaNavi will offer one bull and call out to Hashem, and the Nevi’ei HaBa’al will offer the other and call out to their god. Whichever god responds with fire will be deemed the true God (Melachim I 18:24). There is, however, an apparent contradiction in the Pesukim that describe the Nevi’ei HaBa’al’s execution of Eliyahu HaNavi’s directive.

As noted by Ralbag, Am Yisrael is torn between Hashem and the Nevi’ei HaBa’al and Asheirah. On the one hand, Eliyahu HaNavi’s pronouncement of drought (which lasts for three years) establishes Hashem’s validity. On the other hand, Am Yisrael is heavily influenced by the hundreds of false prophets who operate freely under the aegis of Izevel and Achav. The nation does not respond to Eliyahu HaNavi’s challenge. One could argue that they are embarrassed, or as Rashi and other Mefarshim explain, they are genuinely confused as to the identity of the true God. Once Eliyahu HaNavi presents his fire test to clarify who is the true God, the nation readily accepts Hashem (Melachim I 18:24).

יעננו בקול signifies He answered him in respect to (ב) the voice, just as (1 Kings 18:24) “He that answereth באש” — “in respect to the fire” — i. e. by causing fire to descend. (So here: God answered Moses’ petition that his voice might become audible to the vast concourse of people).