There’s a great line in one of Oliver O’Donovan’s books [Resurrection and Moral Order: An Outline for Evangelical Ethics (Eerdmans, 1994)], where he’s talking about the future resurrection and kingdom of Christ. He says: “Humanity in the presence of God will know a community in which the fidelity of love which marriage makes possible will be extended beyond the limits of marriage.” In other words, one of the good things about marriage now is that it enables two people to make promises to each other and practice the kind of love that doesn’t give up when the going gets tough. It enables fidelity. But, you can’t practice that kind of faithful love with everyone. You’re bound to your spouse, and you don’t love anyone else with the same kind of fidelity. That’s where things will change in the eschatological kingdom of God. Marriage as we know it will fade away, as Jesus tells us in Matthew 22. But the kind of love that marriage pointed to will be the experience of everyone in God’s new creation. And that, it seems to me, is what friendship reminds us of here and now.
In friendship, we can make promises and pursue intimate fellowship with many people, not just one. And in that sense, friendship provides a foretaste of the universal community we’ll enjoy in God’s kingdom. Roman Catholic writer Ronald Rolheiser says that in friendship the central organ of love is the human heart, not the genitals — which means that friendship is a form of love that’s open to all of us, married or single.