"God does not love us as his ultimate happiness. If we were God’s ultimate happiness, he would be needy in relation to us, and his would be demanding of gift rather than the source of all gift. He must, then, ‘use’ us; but Augustine immediately adds that he doesn’t ‘use’ as we do.
When we use a thing, we love it in reference to God. Our goal is to enjoy God for his own sake, and so we do not love other things as our ultimate end, but instead we love them with reference to that end. God loves his own good, and in loving his own good, he loves us as ordered to that good. God’s love of us can be called ‘use’ because he loves us not as his ultimate good but as ordered to that good. He is the divine good, and he wills to share it with us; in this regard he can be said to “use” us, by ordering us to the good that he is.
The difference between his ‘use’ of things and our ‘use’ of things, therefore, is that we use things as part of our journey to attain our end, whereas he already is his end and he uses things to give them their end. . . . The reward that God gives us consists in our enjoyment of God, through which we enjoy each other in God.”
– Matthew Levering, The Theology of Augustine, 7, paragraphing and bold added.