What does Psalm 103:19 mean?

In this verse David declares the idea of God's sovereignty. He has fixed His throne in the heavens and His rule extends to everyone and everything. Lucifer, the Devil, tried and failed to topple the Lord from His throne (Isaiah 14:12–15). Throughout history evil men have followed Lucifer's example, but they, too, have learned the hard way that the Lord is sovereign and invincible. His throne is firmly fixed!

At the end of human history multitudes of rebellious human beings will follow the Devil in a last-ditch effort to overthrow God's rule, but they will not succeed. God will rain fire upon them and consume them, and He will throw the Devil into the lake of fire (Revelation 20:7–10). Unbelievers may be unwilling to acknowledge God, either in submission or by denying His existence. However, James tells us "even the demons believe—and shudder" (James 2:19). God's eternal rule over all should cause His enemies to shudder, but it should bring comfort to believers. He has the will and the power to orchestrate even our trials to accomplish His good work in our lives (Romans 8:28).