What does Psalm 40:9 mean?

David addresses the Lord in this verse, claiming he has proclaimed God's works to others. Those who are in the "great congregation" are presumably the faithful people of Israel. David held nothing back when he reported how the Lord rescued him from his enemies.

When Jesus drove out numerous demons from a man who had been driven by them and existed in a deranged state of mind, He told him to return home "and declare how much God has done for you" (Luke 8:39). Obediently, the liberated man went home and proclaimed throughout the entire city how much Jesus had done for him. Every Christian has a story to tell about how the Lord delivered him or her from sin and judgment. Every Christian is an ambassador for Christ, and through us God is appealing to others to be reconciled to God (2 Corinthians 5:20). The apostle Paul viewed himself as an ambassador for Christ. He testified, "For I am not ashamed of the gospel, for it is the power of God for salvation to everyone who believes, to the Jew first and also to the Greek" (Romans 1:16). Like Paul, we should love to tell the story!