Piper himself notes: "Why did God create the world? Surely not, as some popular theology has it, because he was lonely and frustrated and needed man to make him happy. Before creation, God was, in a profound sense, content in the fellowship of the Trinity. What moved him, then, to create the world? The closest I can come to an answer is this: God was profoundly happy and joyful. But there is in joy an inevitable compulsion or pressure to expand, to extend itself by involving others in it. And this is no deficiency in God, for, as Jonathan Edwards says, "It is no argument of the emptiness or deficiency of a fountain that is inclined to overflow."1 This tendency of joy to expand itself moved God to create beings to share in his joy. Thus creation was a supreme act of love because it aimed at the joy of the creature. But God was not indifferent to his act of creation as if it meant nothing to him. It was his joy in his own perfections that overflowed in the creation of beings to share that joy."
And onwards (ht: Huxley) Douglas Jones offers Trinitarian catechism... some of which is:
Why do they love the dark and not the party?
C. And why does God offer a feast?
D. But what sort of dance is the Lord?
E. Wait, why does God have a wedding?