Elijah's actions around the sacrifice to the LORD God set up a dramatic display of God's power and control over all of creation. Even after the altar is prepared and drenched with water, God rains down fire from heaven and consumes everything. "The Lord, he is God; The LORD, he is God!" goes up the cry after this mighty display. Elijah seizes and kills the prophets of Baal.
You'd think that this would put Elijah on a high that would never end. But it is not so. He had defeated the Prophets of Baal, but King Ahab, and Jezebel did not give up. They threaten him relentlessly. They were still trying to kill him. He had hoped that his victory was sufficient, but it was not. He was very discouraged. He needed extra grace - even after seeing the mighty hand of God powerfully displayed.