Though [God] has real pleasure in the creature’s holiness and happiness; yet this is not properly any pleasure which he receives from the creature.
For these things are what he gives the creature.
They are wholly and entirely from him.
Therefore they are nothing rather a rejoicing in his own acts, and his own glory expressed in those acts, than a joy derived from the creature.
God’s joy is dependent on nothing besides his own act, which he exerts with an absolute and independent power.
And yet, in some sense it can be truly said that God has more delight and pleasure for the holiness and happiness of his creatures: because God would be less happy, if he was less good, or if he had not that perfection of nature which consists in a propensity of nature to diffuse his own fullness.
And he would be less happy, if it were possible for him to be hindered in the exercise of his goodness and his other perfections in their proper effects. But he has complete happiness, because he has these perfections, and can’t be hindered in exercising and displaying them in their proper effects.
And this surely is not thus, because he is dependent; but because he is independent on any other that should hinder him. Dissertation 1 (The End for Which God Created the World), Yale-Works 8:447. (also in Piper’s God’s Passion for His Glory)