The following quote from Augustine is a little thick, a little hard to follow, but it's well worth the time and effort. In short, in order for God to be for us, he must be for himself.
"And on this ground, when we say that we enjoy only that which we love for its own sake, and that nothing is a true object of enjoyment except that which makes us happy, and that all other things are for use, there seems still to be something that requires explanation. For God loves us, and Holy Scripture frequently sets before us the love He has towards us. In what way then does He love us? As objects of use or as objects of enjoyment? If He enjoys us, He must be in need of good from us, and no sane man will say that; for all the good we enjoy is either Himself, or what comes from Himself. And no one can be ignorant or in doubt as to the fact that the light stands in no need of the glitter of the things it has itself lit up. The Psalmist says most plainly, 'I said to the Lord, Though art my God, for Thou needest not my goodness.' He does not enjoy us then, but makes use of us. For if He neither enjoys nor uses us, I am at a loss to discover in what way He can love us.
"But neither does he use us after our fashion of using. For when we use objects, we do so with a view to the full enjoyment of the goodness of God. God, however, in His use of us, has reference to His own goodness. For it is because He is good we exist; and so far as we truly exist we are good...That use, then, which God is said to make of us has no reference to His own advantage, but to ours only; and, so far as He is concerned, has reference only to His goodness" (On Christian Doctrine, Book 1, Chapters 31-32).