The doctrine of the Trinity reminds us that God is the one who authoritatively defines himself. We might imagine that God's love, for example, is defined as a relationship between himself and the world. But then a divine attribute would be dependent on the world. God would have needed the world in order to have an adequate object for his love. But Trinitarianism teaches us that God's love is defined, not by the world, but by the eternal love between the Father and the Son. God would have been a loving God even if he had chosen not to create the world. So God is sovereign in defining his own nature. And he is sovereign, not only in defining his love, but in exercising it. He loves the world, not because he must, but because he chooses freely to do so.
- John M. Frame
(Source : The Doctrine of God)