Lord Melbourne, the 19th-century Prime Minister, once said, after hearing an evangelical sermon: “Things have come to a pretty pass when religion is allowed to invade the sphere of private life.”

In recent times it has rather been the presence of religion in public life that has created controversy. The problem is that religion cannot keep itself to itself. It deals with everyday issues and cannot be disentangled from the fabric of our everyday life.

Christian theology teaches that human beings are created in the image of a Trinitarian God — Father, Son and Spirit. The implications of this are twofold: First, human beings are social creatures, designed to relate to each other and to their Creator. Secondly, human beings are responsible both to God and to one another. In short, we flourish together or not at all.

René Descartes defined the essence of human existence as “Cogito ergo sum” (I think, therefore I am). Contemporary culture tends to subscribe to the philosophy of “Tesco ergo sum” (I shop, therefore I am). Christian theology, however, posits the radical alternative: “I am loved, therefore we are.” This insight is incompatible with either an unrestrained economic liberalism, which can too easily reduce people to the status of autonomous economic units, or with a social liberalism, which sees humans as unencumbered sovereign beings, for whom choice is the supreme good.

One challenge often thrown at people who attempt to inflect public debate with theology is why, in an increasingly plural public space, should anyone take notice of such thinking? The answer is, in part, because most people do, whether we invite them to or not. The world today is as religious as it ever has been, and in some places more so than ever. The majority of people reject the view that a worldwide secular culture is either inevitable or desirable. The “God is dead” school of theology does not resonate with people's experience of the real world. There is a desire for something that is deeper, wiser, more authentic and true. Like it or not, theology is here to stay and will continue to make its presence felt in the public square.

If this is so, we face a serious challenge. Everyone recognises that religion (derived from the Latin religare, meaning “to bind”) has a remarkable ability to divide societies. If theology is set to flex its muscles in public, how can we ensure the public square does not end up looking like a boxing ring?

Christianity has a very particular answer to this. It is a religion, and thus a group of people bound together (although not usually very well, it must be said), but it is a religion in which the binding concept is “the other”.

God, in Christian theology, is supremely holy and, in the words of Karl Barth, “wholly other”. It is not surprising then that the Christian social ethic is based on love of the other. In recognising the grace of God in reaching across the “infinite qualitative difference” to humanity, His creatures are challenged to reach out in a similar way.

It was hardly by accident that Jesus united these two ideas, found in two quite separate Old Testament verses, when asked which commandment was the greatest. “You shall love the Lord your God with all your heart and with all your soul, and with all your mind” and “You shall love your neighbour as yourself.” (Matthew, xxii, 37-9).

Nor was His choice of a Samaritan in His most famous parable an accident. Samaritans were explicitly excluded in contemporary interpretations of the command to love your neighbour. Jesus could not accept that and challenged His audience that there should be no limit to their love. No one was too different, too alien, too other not to be counted as neighbour.

This is how Christian public theology answers the charge of divisiveness. It is also what, at its best, it can bring to public debate. Only the blinkered would claim that religious faith was an unalloyed good. But only the blinkered would seek to bar such a challenging ethical position from public life.

Paul Woolley is the director of Theos, the public theology think-tank