Of all God's infinitely glorious attributes, perhaps his happiness should cause us the most envy. In God is the perfect union of all good things. He has an eternally infinite fullness, delight, and joy in himself — such that we shall never be able to fully appreciate what his joy is like for himself. If God were infinitely good, but unable to effect good because he lacks power, that would make him miserable. If God were merciful and holy, but lacked wisdom to save sinners in a way that does justice to his mercy and holiness, he would also be miserable. If God were not triune, his love for himself would likewise make him miserable. Indeed, if God were eternal, but lacked infinite knowledge, he would be more miserable than those in hell.
As the perfect being, whose attributes all gloriously harmonize with one another, God enjoys a life that is most happy because he has full actualization in his being. Where there is infinite holiness, wisdom, goodness, power, knowledge, and more, there also is infinite happiness.
All Good Things Are in God
If there is any true happiness outside of God in this universe, it is a happiness derived from God. Indeed, according to John Owen, "The human nature of Christ himself in heaven is not [outside of God]; it lives in God, and God in it, in a full dependence on God, and receiving blessed and glorious communications from him" (Works, 1:325).
In addition, the happiness — or "blessedness" — of God must never be considered apart from the triunity of God. His blessedness consists not only in the perfect union of all good things in him, but also in the ineffable mutual love of the three persons. The bond of the Spirit between the Father and the Son brings our triune God infinite joy.
Theologians have not only spoken of God's blessedness as his abounding in all good things, but also as him being free from all miseries (1 John 1:5). But others did not stop there. It was strenuously held by some that we must affirm that God perfectly knows his blessedness. He desires nothing more than what he has because it is impossible for him to be more or less blessed than what he is.