What does Psalm 18:31 mean?

In David's era, pagans worshiped many false gods. The Canaanites often referred to their false gods as their rock; this follows the theme of a foundation or a sturdy base on which to stand. Moses said, "their rock is not our Rock" (Deuteronomy 32:31). David contends in Psalm 18:31 that Israel's God is the Lord and the only Rock, the provider of salvation and security.

Later in Israel's history, when Ahab was king, the worship of the false god Baal flourished. Ahab's wife Jezebel had imported Baal worship and promoted it. She personally provided for Baal's false prophets and tried to exterminate the Lord's prophets. But Elijah, the fiery prophet of the Lord , championed His cause by challenging the Baal prophets to a contest that would determine whether the God of Israel or Baal was real (1 Kings 18:20–39). He gathered the 450 Baal prophets and the people of Israel at Mount Carmel and told the false prophets to prepare a sacrifice and call on Baal. He, too, would prepare a sacrifice and call on the Lord. Whoever answered the call by fire would be declared the true God.

Despite the frantic actions of Baal's prophets, and their prolonged calling on Baal, no fire fell. Yet when Elijah called on the Lord, He answered with fire that consumed the sacrifice and even the torrent of water that Elijah poured on it. When the people saw what had happened, they declared, "The LORD, he is God; the LORD, he is God" (1 Kings 18:39).

In the modern world, so-called-tolerance demands that whatever or whomever a person worships be considered as valid as whatever or whomever anyone else worships. But David's declaration of one true God stands correct (John 14:6). David's God is our God, and He alone is God.