David Cameron would not have had to assert that Britain is a Christian country if the matter were beyond dispute. The worry is that we have embarked on a journey of moral drift in this particular sense: it is not that Christian morality makes all things good – far from it – but it has the capacity to bring all things to account. To put it in more philosophical terms, theistic ethics can sustain an objective quality – something recognised by ethical thinkers as diverse as Friedrich Nietzsche and Pope Benedict.

Again, it's worth reflecting on what is meant by objectivity. It is not that rights and wrongs become self-evidently clear. Even so-called divine command theory – right is right because God decrees it is right – urges believers to engage in the arduous task of discerning just what God decrees as right. This is because God's moral law cannot be read off the page, in spite of what some might tell you, but can only be comprehended by those who have undergone a lengthy process of training and transformation. As Saint Augustine prayed: "Lengthen my days for the study of your law's inner meanings. Open the door to them when I knock on it. You had a purpose in causing the Scripture to contain so many pages dark with obscure meaning." Light comes when the individual's will is aligned to God's will, a lifelong task for which even the saint had to ask more time.

So objectivity in ethics is valuable not primarily because of what it might tell us to do, but because of where it suggests we might be heading. It is a view of morality that stands over and above the human frame. Only an ethic not of our own making can truly call us to account; and further, only an ethic not of our own making can remake us and surprise us. (I can't help but feel that this is what really offended Christopher Hitchens about Christian morality: it told him he was not a god and then, adding insult to injury, that he needed God.)

Iris Murdoch, the novelist and philosopher, made the case for such a transcendent view of morality in her book The Sovereignty of Good. The middle chapter, On "God" and "Good", pays re-reading. She calls it having an eye for a wider horizon. It draws the individual's inner gaze towards goods that are beyond their imagined concerns, though might be of concern to them because the wider horizon promises a flourishing that humanity, of itself, could never divine.

Think of the life of the artist, Murdoch suggests. The greatest artists are not self-aggrandising but other-attending; they don't use their imagination to pursue agendas but to open reality. The great test is whether the artist disappears in their art or whether they stamp themselves all over it. "The greatest art is 'impersonal'," Murdoch says, "because it shows us the world, our world and not another one, with a clarity which startles and delights us simply because we are not used to looking at the real world at all."

The moral life springs from that sight because it is fundamentally a question of attention, not action. It is about what you focus on before what you decide to do. This explains why moral heroes often tell of a striking event that etched itself on their mind. Desmond Tutu writes of seeing the white bishop, Trevor Huddleston, doffing a hat to his mother. In an instant he glimpsed a different world, a wider horizon. Such moments cannot be contrived, though they are presumably all around to those with the eyes to see.

I sense that this is why so much of what passes for moral philosophy today feels like it misses the point. Take the oft-discussed "trolley problem". It proposes thought experiments featuring runaway trolleys and innocent bystanders some of whom must die, depending on what you decide. But do such scenarios model moral life at all? They treat ethics as an isolated event, as a calculation: "The agent, thin as a needle, appears in the quick flash of the choosing will," Murdoch writes.

In truth, though, the moral work of our lives is done continually, collectively and over time. It emerges in the shape of our personality and temperament, habits and character. Prayer and meditation are more likely to nourish the good in us than reason or dispute. The religious sensibility understands that deeply, too, another reason it might be valued by those who have a concern for the moral life of our times.