I have always looked at it as having joy in the Lord, or rejoicing in the Lord. IOW, our full and consummate joy will always be in the Lord, and in no other. The analogy of the bridegroom and bride is a beautiful picture to behold and sort of sums up the kind of eternal bliss that we will enjoy being in the presense of the Lord.
And I would say that God is not without His joy either. It says, "for the joy that was set before Him, He endured the cross, despising the shame." Or, Isaiah 62:5, "For as the young man marries a young woman, so shall your sons marry you, and as the bridegroom rejoices over the bride, so shall your God rejoice over you."
And other places in the Confession and catechisms lend a thought or two, especially in talking about the eschatological state of the elect; "to the full enjoying of God to all eternity." But even now, as a benefit of justification, adoption, and sanctification we have, "joy in the Holy Ghost."
So I would say that the joy is mutual, although much more on our part. And even in that joy, we would never say that we fulfill God in some way, or in some way He is lacking joy until the consummation of all things. But just as Boaz, the kinsman-redeemer, probably did experience joy in having Ruth as wife, the joy of Ruth, and the mercy and grace she was shown as a Moabitess, gives us a great example of our own kinsman-redeemer in whom we have immense joy now, and even more blissful joy in Heaven.
Kevin C. Easterday
Ruling Elder Westminster PCA, Jacksonville, FL
M.Div. Greenville Seminary
Husband to Tina (August 13, 1988), Father to Kamden (22) and Kolton (21)