I LIVE in San Francisco, unofficial capital of America's secular obsession with food. Sometimes I think I'll lose my mind if I hear anyone say "organic","local", or "artisan" again. Having been converted to Christianity by communion bread and written a book about it, I'm even more cynical about the religious values we assign so glibly to food. Does buying all-organic groceries make you a better person? Does being careful about how much sugar your kids consume bring you closer to God? Can kale save?

It's a short step from imagining that your food choices about humane, sustainable agriculture will justify you, to believing that other people who don't eat the way you do are living in sin. But poor immigrant kids eating salty crisps, and white middle-class social workers eating soy yogurt, and businessmen eating big industrial slabs of beef - we are all in a state of sin. And food will not save any one of us.

God will save us.

Yes, contemporary food systems are sick. But our healing and that of our communities can't come about solely through technical interventions around agriculture, political campaigns to improve the quality of the foods we eat, or an anxious focus on organic cleanliness. Real healing requires communion: that is, sitting down and eating with others - especially with strangers, and the impure, as Jesus does.

GREGORY OF NYSSA, the patron saint of my home church, was a bishop in the fourth century in what is now Turkey. Here are his strikingly contemporary words on faith and food, from his sermon on the Lord's Prayer:

"So we say to God: Give us bread. Not delicacies or riches, nor magnificent purple robes, golden ornaments, and precious stones. . . We do not say, give us a prominent position in assemblies or monuments and statues raised to us, nor silken robes and musicians at meals, nor any other thing by which the soul is estranged from the thought of God; no - only bread!

"But you go on business to the Indies and venture out upon strange seas; you go on a voyage every year only to bring back flavourings for your food, without realising that it is, above all, a good conscience which makes the bread tasty because it is eaten in justice.

"'Give us bread' - that is to say, let me have food through just labour. For, if God is justice, anyone who procures food for himself through covetousness cannot have his bread from God. You are the master of your prayer if your abundance does not come from another's property, and is not the result of somebody else's tears; if no one is hungry or distressed because you are fully satisfied. For the bread of God is, above all, the fruit of justice."

GREGORY'S use of the first person plural is Gospel. Not "give me bread", but "give us bread". Not "I", but "we". Not "my self", but "our body".

Every Friday, at the church named for Gregory of Nyssa, after singing the Lord's Prayer at the morning service, I go with our priest Paul Fromberg to shop at the upscale Whole Foods store around the corner, so we can prepare lunch for the more than 50 volunteers who run our food pantry.

The volunteers come from the streets and slums; they're foreigners; they're hungry, and poor. They work all day giving away food to strangers: they unload pallets and set up tables overflowing with bread; they lift sacks of potatoes and break down boxes and deal with the public - it's hard work. So Paul and I always cook a full, hot meal for the volunteers, and everyone shares it before the pantry opens.

Each week, Paul and I stroll down the aisles of Whole Foods, arguing about what to cook, and I gaze at the incredible variety: tiny jars of pink peppercorns, and displays of organic sheep's-milk cheeses from around the world, and shelves overflowing with 19 varieties of salt. I look at the figs from Spain, and the saffron from Kashmir, and I hear Gregory sadly saying:

"But you go on business to the Indies and . . . go on a voyage every year only to bring back flavourings for your food, without realising that it is above all a good conscience which makes the bread tasty because it is eaten in justice."

Of course, I love flavourings from the Indies, too, and delicacies and riches, and cooking big splashy meals. But sometimes the excess makes me nervous: it's not what food is for.

ONE DAY I noticed Paul had picked up special expensive supplies to make a three-layer cake; then, while I was busy with the soup, he made a complicated meringue-based icing; and while I was rushing to get the casserole in the oven, he began decorating the whole thing with crushed praline dust and beautiful little pastry-cream rosettes.

"What's up?" I asked, kind-of-irritated that Paul was taking so long fussing with decorations when we had 50 hungry people waiting for lunch. Paul shrugged. "Somebody told me it was Matthew's birthday," he said. Matthew, who works unpaid 20 hours a week as the director of operations for the food pantry, is an undocumented Irish immigrant without a bank account; a former heroin addict who got clean in prison. He's impossibly generous: he barks gruffly at everyone, but then gives away the food he gets from the pantry. Matthew has missing teeth and homemade tattoos and would probably set off security alarms at Whole Foods.

God, Gregory of Nyssa wrote, desires relationship with us; and we desire relationship with God, and with other humans. This is what food is for. Paul stood back and admired his handiwork. "You know, when Matthew was in jail," Paul said quietly, "I bet he never imagined anyone would bake him a birthday cake again. So I wanted to make it special."

WHAT makes our bread tasty? The love of God, which is the love of all God's people. And so we say to God: "Give us bread."

Gregory, down the years, teaches that faith is not abstract, but requires us to act - that our faith has material as well as philosophical consequences. We say over and over in church that we are the body of Christ. Yet if one part of the body enjoys flavourings from the Indies while another part is starving, then that body is sick.

And what can possibly heal us? Bread. The simplest loaf or the fanciest pink birthday cake, if it is eaten together in justice. Not justice in the sense we mean when we reduce social justice to an "issue" - the formulaic justice of this world - but overflowing justice, based on the undivided life of God.

So give us that bread, we pray, which transforms us, as we share it with others, into one body.

Sara Miles is the founder and director of The Food Pantry, and author of Take This Bread: A radical conversion.