Since faith is the source of our worship of God and the foundation of that doctrine which is according to piety, it dictates that we should conceive of God in the most elevated and most loving manner. Now our thought would not be the most elevated if we did not believe that God could communicate himself in the most complete way, and it would not be the most loving if, believing him so able, we thought him unwilling to do so. Hence, if we are to think of God most loftily and most lovingly, faith tells us that God totally communicates himself by eternally having a beloved and another who is loved by both. In this way God is both one and three.
In fact, the whole of Sacred Scripture, which is called a doctrine according to piety, testifies to this belief, dictating that we conceive of God in the most loving way. For it declares that God [the Father] has an offspring whom he supremely loves: a Word coequal with himself, whom “he has begotten from all eternity and in whom he has disposed all things,” by whom he produces and governs all things. Furthermore, it declares that through the precious blood of this Word made flesh, God in his all-surpassing goodness redeemed humankind and nourishes it once redeemed. It also declares that at the end of the world, through that same Word, God will liberally pour out his supreme mercy, delivering humankind from every misery, so that through Christ, all the elect might become children of the eternal Father. In him all love will be consummated: God’s for us, and ours for God.
And that our faith requires that we think of God in the most elevated manner is attested to not only by Scripture, but by all creation as well. As Augustine writes in the fourth chapter of his fifteenth book On the Trinity: “It is not, after all, only the authority of the divine books that asserts that God is. The universal nature of things which surround us, to which we too belong, proclaims that it has a most excellent founder, who has given us a mind and natural reason by which to see that living beings are to be preferred to non-living, ones endowed with sense to nonsentient ones, intelligent ones to non-intelligent, immortal ones to mortal, powerful to powerless ones, just to unjust, beautiful to ugly, good to bad, things that cannot decay to things than can, changeless to changeable things, invisible to visible, non-bodily to bodily, happy to unhappy. And so, since we rank the Creator without a shadow of doubt above created things, we have to admit that this being supremely lives, and senses and understands all things, and cannot die, decay, or change; and that it is not a body but the most powerful, just and beautiful, the best and happiest spirit of all.”