Among other works which are to be attributed to him, God has formed moral agents. Of all his various works, this is, in some respects, the greatest. He has formed angels; he has formed men. The mere fact that he has made them, which involves the additional fact of the relationship of cause and effect, in other words, of father and child, constitutes an alliance, which is both an alliance of morality and an alliance of the affections In other words, he is allied to them by duty and allied to them by love.
If God is a good and holy being, it is not possible for him to create a being or beings susceptible of happiness, without making provision for their happiness, and without rejoicing in their happiness. To be indifferent to and not to rejoice in the happiness of his creatures, would be the characteristic of an evil and not of a good being. But no moral being which God has created can be truly and permanently happy without loving God and all other beings as God would have them love; in other words, without being holy. We come, then, to the conclusion, that another and very great source of God’s happiness is the contemplation of the holiness and happiness of his creatures. If they are holy, they cannot be otherwise than happy; and if they are happy, God must be happy in them.
— edited from A Treatise on Divine Union (1851) Part 7, Chapter 12.