What does Psalm 21:1 mean?

This may contain David's words spoken in the third person, or the statement of the assembled people. In either case, they express David's joy over the Lord's power on his behalf. He rejoices in the Lord's deliverance of him from his enemies. In the previous psalm he had prayed to be delivered, and now he thanks the Lord for answering his prayer.

Believers ought to pray and then thank the Lord for answering their prayers. David credits the Lord's strength for the deliverance and rejoices because of the Lord's strength. We, too, can rejoice in the Lord's strength that delivers us in our time of need. Jesus said we will have joy if we keep His commandments (John 15:10–11). If we obey our Lord and place our confidence in His strength and not in our own strength, we can be strong. Paul attributed his victories to the Lord's strength. He wrote: "For the weapons of our warfare are not of the flesh but have divine power to destroy strongholds" (2 Corinthians 10:4).