The first few years of this century are turning out to be busy ones for anti-religious polemicists. Richard Dawkins’s The God Delusion and, soon to appear, Christopher Hitchens’s God is not Great revive a tradition of impassioned criticism of religious belief and of what people do in God’s name.

The reason for the relative quiet in the closing years of the last century is plain enough. As long as religion had seemed to have little to do with anything important – such as politics or war – committed secularists were spared the bother of arguing that religion is bad. It is only when people do bad things in the name of their religious beliefs that atheists need to get evangelical about their creed.

Personally, I don’t feel any desire to leap to the defence of Christian faith against this renewed assault. This is not because others are doing the job well enough, but because, Christian though I am, I have some sympathy with the view that belief in God can be dangerous.

If God is not to be abused, it seems important to me to recognise that religious belief can be dangerous for individuals and for society. The fact that most of the time religious convictions in practice make believers good neighbours and good citizens does little to lessen the scandal when God is invoked to justify tyranny or terror.

In my experience people who are serious about religious faith often best understand its dangers. And the danger is that the lines separating sainthood from madness, or dogma from dogmatism, are fearfully fine and it is not always easy to tell on which side of them I, or my co-religionists, are travelling.

One obvious reason why it is so hard to distinguish good faith from bad faith may be, according to one Christian account, because evil has a knack of deliberately mimicking the good in order to cause confusion. Evil, that is, is often at its most effective when it dresses in religious clothes.

No one has imagined this truth more vividly than the poet Dante Alighieri, whose Divine Comedy pictures a journey made by the poet through Hell and Purgatory to Paradise. In the deepest pit of Hell the poet sees the giant figure of Satan, whose terrible form is a grotesque of God, a parody of divine power. In a travesty of the Trinity, Satan has three faces and, in an inversion of the self-giving of Christ’s body and blood in the Eucharist, in each of his three mouths he devours a sinner. But the full force of what Dante imagines is not brought out until the final stanzas of the poet’s journey through Paradise. It is only when the poet sees the true God that the extent of Satan’s mimicry becomes apparent. The poet writes (in Dorothy Sayers’s translation):

That light supreme, with its fathomless

Clear substance, showed to me three spheres, which bare

Three hues distinct, and occupied one space;

The first mirrored the next, as though it were

Rainbow from rainbow, and the third seemed flame

Breathed equally from each of the first pair.

The horror of the three faces of Satan is finally erased by his vision of the Trinity, and the poet’s last word is that:

My will and my desire were turned by love,

The love that moves the sun and the other stars.

Trinity Sunday, which falls tomorrow in the Christian calendar, draws the eye towards the most fundamental of all the Church’s convictions: that there is only one God in Trinity who is eternally and unchangeably Father, Son and Holy Spirit, and who turns will and desire to love. A Christian is one in whose life this Trinitarian love is at work. It is this which distinguishes genuine disciples from those who would steal their clothes in grotesque mimicry of religious faith.

Stephen Plant teaches theology in Cambridge