This psalm, addressed to the Lord, concerns the Lord's own enemies as well as those of David, the king of His people Israel. Of course all concerns of David, are concerns of the entire covenant nation, and all the enemies of the Lord are enemies of His people as well.
The psalm, then, is really not merely a psalm of David, but also a psalm of the people, and it was therefore a very appropriate song for them to sing when they gathered in the morning at the tabernacle. It's still appropriate today for the New Covenant people of God.
Though David isn't our king today, his greater Son, our Lord Jesus Christ, is King of His church, so we too can join in and repeat after the worship leader, "The King shall have joy in Your strength, O Lord; and in Your salvation how greatly shall He rejoice!" Our Lord Jesus Christ in His manhood rejoiced in the strength of His Father, and, having accomplished His people's salvation, He rejoiced greatly in that as well! He can and does sing, "You have given Him His heart's desire, and have not withheld the request of His lips." (See also Isaiah 53:10-12)
The song describes blessings received by our Lord at His resurrection and ascension to the right hand of His Father. He sings, "For You meet him with the blessings of goodness; You set a crown of pure gold upon His head. He asked life from You, and You gave it to Him - length of days forever and ever. His glory is great in Your salvation; honor and majesty You have placed upon Him, for You have made Him most blessed forever; You have made Him exceedingly glad with Your presence, for the King trusts in the Lord, and through the mercy of the Most High He shall not be moved!"
So this is a victory song, a song sung as the victorious King returns to the palace - whether in David's day or our own. But it's not joyful for His enemies. They cannot escape Him. He sings, "Your hand will find all Your enemies; Your right hand will find those who hate You." He continues in a like vein, expressing that these enemies are going to meet justice at the end when all evil is cleansed away. It should remind us of David's words elsewhere (Ps. 110, Matt. 22:44), where he says, "The Lord said to my Lord, 'Sit at My right hand 'till I make Your enemies Your footstool!"
And, finally, all the people of God join together in the final chorus to sing, "Be exalted, O Lord, in Your own strength! We will sing and praise Your power!"
Do you join in this joy of your Lord, the joy of victory over sin and the Devil? Are you glad in His gladness? And are you joyfully awaiting the day when He returns to make that complete victory plain to all men and angels?