Second, in his most important work, City of God, Augustine explains the inadequacy of earlier philosophical notions of friendship like Aristotle’s that do not culminate in an eternal friendship with God. He recognizes that philosophers arrive at some truths, such as the creation of the world by God, “the nobility of virtue[s],” or “love of country and loyalty in friendship.”¹¹ However, he expresses his concern that “they were ignorant of the end to which all these were to be referred and the standard by which they were to be assessed.”¹² In other words, ancient philosophers, including Aristotle, Cicero, and many others, failed to understand that a loving relationship with God is the ultimate purpose and end by which love of others is given lasting significance.

After pointing out the failure of a purely philosophical approach to friendship, Augustine contends that Christian Scripture reveals that friendship with God the Father, which can only be obtained through the forgiveness and mediation of Christ, is the highest good. But before explaining exactly what Augustine means, we have to understand a couple other important assumptions he makes. The first is that Augustine did not accept that contemplating God as the highest good would itself lead human persons to virtue and happiness. Human desires are misdirected and, according to Augustine, people are unable to correct them by themselves. Second, for Augustine, happiness is not perfect unless it has the built-in guarantee that it will not fail or collapse. Perfect happiness, the best that we can wish for a person, is not transient or finite, but consists in an eternal relationship with God. Matthew Levering provides a helpful sketch of this concept when he writes that “[f]riendship can be enduring only when our relationship to our human friends is caught up in our relationship to God.”¹³ It is only on the other side of Christ’s second coming and the divine judgment, in the direct presence of God, that Augustine believes people can be truly and finally satisfied in unremitting joy. In this way, Augustine’s vision for the Christian life culminates in friendship of the most profound and lasting kind, namely, with the Triune God.¹⁴

In the tenth book of City of God, Augustine unpacks his understanding of Christian friendship in terms of what Jesus calls the two greatest commandments:

We are commanded to love this Good with all our heart, with all our soul, with all our strength; and to this Good we must be led by those who love us, and to it we must lead those whom we love. Thus are fulfilled those two commands on which “all the Law and the prophets depend”: “Thou shalt love the Lord thy God with all thy heart, with all thy soul, and with all thy mind,” and, “Thou shalt love thy neighbor as thyself.” For in order that a man may know how to love himself an end has been established for him to which he is to refer all his action, so that he may attain to bliss. For if a man loves himself, his one wish is to achieve blessedness. Now this end is “to cling to God.” Thus, if a man knows how to love himself, the commandment to love his neighbor bid him to do all he can to bring his neighbor to love God. This is the worship of God; this is true religion.¹⁵

For Jesus, Augustine, and the Christian, we must be lovers of God and lovers of others. As with loving ourselves, loving another person means loving them in such a way that they will love God and thereby put their future hope in eternal life with God. This is Augustine’s central insight. He integrates the philosophical tradition of loving others for the sake of the good with the heart of the Christian faith, loving God and loving others.

Augustine’s emendation of Aristotle on friendship is that our friendships should have as their primary aim leading others and ourselves to eternal life in communion with God. The truest form of friendship will account for both the horizontal and the vertical planes. Our vertical friendship with God organizes our horizontal friendships with others. As we begin and participate in friendships with people, the things we do together and the ways we relate to one another ought to be aimed at helping the other person grow in faith, hope, and love. As we configure our lives to the shape of Christ’s life, seeking to know and love God more each day, friendship consists in seeking the same growth for our friends, whether they love God or we hope they will come to love God. For Augustine, the context of the community of friends working together to cultivate love for God is always the church.

While Augustine identifies some higher goods to be used and enjoyed, such as health, wisdom, and friendship, there is a single object of true enjoyment, for the sake of which we make good and proper use of created objects.¹⁶ This single object is the triune God who through the Son and the Spirit enables us to know and love God in this life so that we can see God in the next.¹⁷ Just as we use study and learning to enjoy wisdom, we use friendship to enjoy God. For Augustine, to sin is to prioritize a lower good (e.g., a creature) over a higher good (e.g., the Creator), for example, to put study above wisdom or friendship above God. Even more, while Augustine says that we ought to use things “to help and sustain us as we move toward blessedness,” he does not—and cannot—mean that in the context of friendship we should use another person in a destructive fashion.¹⁸ In loving God we cannot abuse or otherwise harm someone. When the manner of use is destructive, the true object being sought cannot be good. Just as cheating on an exam is not seeking to enjoy wisdom, so too causing harm to a friend is not seeking to enjoy God.

Augustine offers at least three modes of Christian friendship that make important strides beyond the work of Aristotle. First, there is the form of Christian friendship in which we treat others in a friendly manner, loving them the best way we can to help them grow in their knowledge of and love for God. Such relationships are usually with people who are not in our inner circle because more often than not our love is not reciprocated, at least not in a way that helps us grow in faith, hope, and love.