Immediately, Elijah challenged the prophets of Baal to prove, once and for all, that Jehovah was not the one and only true God; but their gods could not respond because they did not exist (1 Kgs. 18:19-29). Notice that the false prophets tried from the time of the morning sacrifice (Sunrise - Lev. 9:17; Num. 28:8), until the time of the evening sacrifice (Sunset - Ezra 9:5; Ps. 141:2), but to no avail (v. 26-29).
Apparently, near the end of the day, Elijah had the people repair, and prepare, the alter of the LORD for his sacrifice, because at the time of the evening sacrifice, Elijah's sacrifice, the alter, and the twelve barrels of water, were consumed by fire from God (1 Kgs. 18:30-38)! The people of Israel were truly convinced, and they must have been terrified; "And when all the people saw it, they fell on their faces: and they said, The LORD, He is the God; the LORD, He is the God" (v. 39). The Hebrew for "the LORD" is יְהֹוָה (Yĕhovah), and for "the God" is אֱלֹהִים ('elohiym).
The Prophet Malachi foretold that Elijah, who did not die (2 Kgs. 2:11), would return to prepare the way for Israel's Messiah (Mal. 4:5). Had Israel received Jesus at His First Coming, John would have fulfilled that prophecy (Mt. 11:7-15; 17:10-13; etc.). John's ministry is described in Matthew 3:1-12, Mark 1:1-8, Luke 3:1-20, and John 1:19-28; 3:25-36; and while both Elijah's and John's ministries were similar in their confrontation with the corrupt leaders of Israel, John's results were sadly different (Mt. 14:1-12; etc.).
Because Malachi's prophecy has yet to be fulfilled, it is widely accepted that one of the Two Witnesses of Revelation 11 has to be Elijah. He will confront the Antichrist (v. 3-12), he will burn his enemies (v. 5), he will stop the rain (v. 6), and his death will fulfill Hebrews 9:27. And, while I cannot prove this, I believe Elijah's preaching for a thousand two hundred and threescore days (v. 3), coupled with the Abomination of Desolation (Dan. 9:27; Mt. 24:15; Rev. 13:6), causes Israel, once again, to cry out "The LORD, He is the God!"
Elijah: God's faithful prophet of both the Old and the New Testaments!