Friendship is a wonderful thing. Christian friendship is infinitely better. In fact, I think it would be correct to say that only Christians can experience true friendship.
From a biblical standpoint, one’s will and affections are ultimately rooted in his heart. If the heart of an individual is unregenerate, his only love is self-love; he only seeks his pleasure, his heart is proud, and he delights in evil. His will and affections, then, from whence friendship must flow are perverted.
But the heart of a Christian is different. The heart of a Christian is primarily oriented towards the worship and enjoyment of God. From this type of heart, friendship will simply be a partnership in achieving this goal. In other words, a friend is one who loves God by displaying God to me, that in our friendship I might see more of God and thus love God more. In our friendship, I will enjoy God to greater degrees than I had previously known, because I experience the life of God and the mercy and love of God in my friendship with another Christian.
It is at this point in particular (the theocentricity of friendship) where Augustine departed from philosophers who had come before him and had attempted to define true friendship. “While friendship by classical writers is described as a search together for beauty, truth, and wisdom, in Christian friendship, the search ultimately leads friends to the source who is Beauty, Wisdom, Truth, and Love.” God being the ultimate object of all human desire is not a new theme to Augustine in the Confessions, but here it is introduced as the very basis of all Christian friendship: Helping one another pursue our Sovereign Joy.
Perhaps the most profound element of friendship in Augustine’s thought is the idea that in friendship, one will fulfil the twofold commandment. Augustine here adapts Cicero’s definition of friendship, which involved simply doing what is best for the other person, in a reciprocal relationship. “If God is seen as the highest good towards which everything must be directed and if all love must focus on God before all else for it to be truly Christian, friendship among Christians gains a new perspective.” For Augustine then, you are loving God and loving another as yourself by helping him to love God, which is his greatest good, which in turn he will do for you, as this is your greatest wish for yourself as well. Friendship for friendship’s sake—even friendship for the other person’s sake—is no longer in view at all in Augustine’s thought.
This friendship which is centred entirely on God and his goodness benefits all involved by helping them to gain a clearer vision of him. “Sage has observed that the anima una ‘est pour S.Augustin, à partir de 407, l’énigme et le miroir par excellence où il nous est donné dès ici-bas à comprendre, comme nous le pouvons, le mystère de Dieu’.” To Augustine, the most valuable friend in the world is the one who can best reveal God to him and push him to pursue God. In short, “Augustine thinks of friendship as beginning, continuing and ending in God—friendship is participation in the life of God.”
Augustine never reached the goal of friendship he desired in this life, because what he desired was none other than God himself, and the pure unadulterated fellowship with fellow humans which flowed out of that. “His ideal was no earthly society but a heavenly community of mutually loving members of the City of God (described as ‘a perfectly ordered and perfectly harmonious fellowship in the enjoyment of God and a mutual fellowship in God’) and only here would men be able to know one another completely and to form a perfect intimacy, as friends aimed to do.” But that day has now come for Augustine, and will soon come for us. The lesson for us in the meantime is to pursue God and to pursue friendships in which we can push others in their pursuit of God and find ourselves encouraged as well—and to do so with all the strength and vigour that Augustine did.
For more on this, see here.
 Carolinne White, Christian Friendship in the Fourth Century (Cambridge: Cambridge University Press, 1992), 197.
 As quoted in White, Christian Friendship, 210.
 White, Christian Friendship, 205.