1 The king rejoices in your strength, Lord. How great is his joy in the victories you give!
2 You have granted him his heart’s desire and have not withheld the request of his lips. 3 You came to greet him with rich blessings and placed a crown of pure gold on his head. 4 He asked you for life, and you gave it to him— length of days, for ever and ever.
This Psalm seems to be a companion Psalm to Psalm 21, where the people of God prayed for King David's victory in battle. This Psalm gives thanksgiving for the victory God gave King David, and the great joy David experienced because of the strength God gave him. Notice the word "joy" is used two times in the first verse.
There is a joy that comes to us when we have completely trusted in God for a battle, and he delivers us and we are victorious. Not only are we glad that the battle has been won, but we have joy knowing it was the Lord who gave us the victory. God not only answered David's prayer, but also granted him his heart's desire. God is not against desires especially as they are submitted to Him. As Psalm 37:4 says, "Commit your way to the Lord will give you the desires of our heart!"
Finally, these verses end with images of the King David with crown on his head, and the gift of not only life now but forevermore. David's life was blessed, and His kingship was passed through the Davidic line all the way to King Jesus, 14 generations later. Jesus, the King of Kings, would provide the victory over our enemies that would lead to eternal life!