O LORD, in your strength the king rejoices, and in your salvation how greatly he exults!
…For you make him most blessed forever; you make him glad with the joy of your presence. —Psalm 21:1, 6
In this psalm, the people of God rejoice in their king’s rejoicing. The people are rejoicing, but they are not singing about their joy, and yet it is their joy. The salvation the king exults in is their salvation. His joy is their joy. When David is saved, the kingdom is saved.
As this is fulfilled in Christ, it speaks to the joy that was set before Christ, for which He endured the cross (Hebrews 12:2). This is not simply the eternal and infinite joy that the Son has always had in the Father. This is the joy which follows the Son’s salvation, meaning the deliverance from and destruction of His enemies (Psalm 21:8–13). This the the joy that falls on the incarnate Christ, our King, who acts as our covenant head. When He is “anointed… with the oil of gladness beyond [his] companions,” that oil covers His people who are in union with Him in the Spirit. His salvation is our salvation. His joy is our joy.
In John 17:13 Jesus prays that His joy might be filled in us (cf. John 15:11). Is there any joy like this? Spurgeon comments, “The rejoicing of our risen Lord must, like his agony, be unutterable. If the mountains of his joy rise in proportion to the depth of the valleys of his grief, then his sacred bliss is high as the seventh heaven.” Here we see the highest joy, the infinite God delighting in what is infinitely delightful. But again, we are not seeing the Triune God’s joy as it has always existed, but as it is in the redemption of man. This is no self-contained joy. This is a joy we are invited into.