God is happy. Being infinite, he is infinitely happy. And it is interesting to know that holy beings, in whatever parts of the universe they exist, constitute one of the elements of the divine happiness. This being the case, there is such a thing (and it is certainly a most interesting and important consideration) as being united with God in the promotion of his own happiness. The humblest soul, when purified by divine grace, becomes a gem in the crown of the Infinite Father's bliss.
Undoubtedly the elements of the divine happiness are various. God, for instance, is happy in the knowledge of his own perfections; and especially is he happy in the consciousness that the central principle or life of his nature, that which brings the infinity of his natural attributes into action, is holy love. Most readily do we admit that he rejoices in his natural attributes also, in his inherent and universal knowledge, in his omnipresence and omnipotence; but more than all and above all does be rejoice in that living and life-giving principle, which saves his merely natural attributes from evil applications, and renders them available to the highest purposes.
And the exceeding happiness which God thus experiences is not the result exclusively, nor chiefly, of a reflex act. Some writers seem to suppose (at least such would be the interpretation of their language if taken in its natural and obvious import) that God sits alone in an infinite solitude, and is happy chiefly by means of such an act; that is to say, by means of the mind turned back in acts of contemplation on its own inward nature. It seems to us better, and more in accordance with the divine nature, to say that God is happy, not so much by a series of reflective and deductive acts, as by direct consciousness.
Consciousness of happiness takes place when the happiness, flowing out naturally and necessarily from the existing states of the mind, pervades the mind and makes itself known without any care or effort on the part of the percipient subject. He, who loves with pure love, is happy; because happiness is a part of love's nature. Happiness, although there may be causes of affliction, which will diminish the amount of it at times, never was separated and never can be separated, from love. To speak figuratively in the matter, happiness is the smile of love, and it sits just as naturally and beautifully upon love's countenance, as the smile does upon the countenance of any pure and benevolent being. Or, to use another illustration, it is love's bright and eternal seal engraven upon it with letters of light. They are thus connected by an eternal relationship. And God can be no more unconscious of happiness in love, than he can be unconscious of love itself.
— edited from A Treatise on Divine Union (1851) Part 7, Chapter 12 by Thomas Cogswell Upham. You can find more of his work at the blog, The Hidden Life, managed by Craig L Adams at: http://thomascupham.blogspot.com