Peter Lombard, Sentences, Book II:
And if it is asked for what is the rational creature created, answer: to praise God, to serve him, to enjoy him. By these things, the creature profits, not God. For God, who is perfect and filled with the highest goodness, can be neither increased nor diminished. And so God’s making of the rational creature is to be referred to the Creator’s goodness and to creature’s utility.
And so, when it is asked why or what the rational creature has been made, it may be answered most briefly, because of God’s goodness and for its own utility. For it is useful for it to serve God and enjoy him. And so the angel or man is said to have been made for God: not because the creator, God and most highly blessed, needed the service of another, since he does not need our goods; but so that the creature might serve and enjoy him, to serve whom is to reign. For in this it is the servant who benefits, and not the one who is served.