We Christians have had a lot to thank Terry Eagleton for. Not only did he write, in Reason, Faith and Revolution, the most enjoyable response to the new atheism, but he's now published another thoroughly enjoyable book that all but restores evil to its rightful place.

Evil has done rather badly in recent years, being often ignored by  and unintelligible to  the chattering end of culture. This is in some ways surprising, because out in the field it has been performing as strongly as ever. No longer talked about much in polite society, it emerges, luridly, in tabloid commentary. And it is here that Eagleton begins his examination, with the murder of James Bulger and the proclamation of Jon Venables and Robert Thompson as embodiments of evil. A policeman who worked on the case remarked: "As soon as I laid eyes on him [Thompson], I knew he was evil." This is the kind of thing, Eagleton says, that gives evil a bad name.

Like a theologian, Eagleton loves paradoxes, and for someone who has spent a lifetime in the Marxist vanguard he strikes me, moreover, as a deeply Catholic writer. He certainly seems to have Catholic literary tastes, examining the theme of evil in the works of, among others, Graham Greene, Flann O'Brien and Pierre Choderlos de Laclos, whose Les Liaisons Dangereuses encourages Eagleton to comment: "There is good reason to believe that the devil is a Frenchman." Eagleton reserves special scorn even for the doyen of French Marxist intellectuals, Jean Paul Sartre, zeroing in on Sartre's notorious line: "Hell is other people." Wrong, says Eagleton. "It is exactly the opposite. It is being stuck for all eternity with the most dreary, unspeakably monotonous company of all: oneself."

Sometimes his thinking is less straightforward. He once described the witches of Macbeth as a sisterly community on the shadowy borderline of a status-obsessed regime. This not only makes Birnam Wood sound like Greenham Common but ignores the sheer devilry of the witches' doings. In On Evil he partly revises this: "Their negativity is one which finds positive existence itself abhorrent."

This goes to the heart of what Eagleton understands evil, rather than wickedness, to be. "It is supremely pointless. Anything as humdrum as a purpose would tarnish its lethal purity. In this, it resembles God..." Evil aspires to God's creativity but reverses it, turning the gift of being into non-being through various techniques of annihilation. Evil, however, can only annul what has already been brought into being and cancelling what is created only intensifies our sense of the sheer goodness of being. This drives its agents mad, and their destructiveness, where circumstances permit, reaches unimaginable pitches of frenzy if they don't consume themselves first. Evil is sulky, Eagleton concludes.

He also questions an idea that is now commonplace  that evil is glamorous. We admire people, Eagleton admits, who "thumb their nose at authority, but not rapists or corporate fraudsters". Our feelings may be more complex than that  Don Juan, for example, elicits contradictory emotions. Some of Eagleton's distinctions invite further questions: "Two actions may look the same, but one may be evil and one may not. Think, for example, of the difference between someone who practises sadism for erotic pleasure in a consensual sexual relationship, and someone who forces excruciating pain on another person in order to assuage his own nauseous sense of non-being." I am not sure that it is always so easy to tell the difference. Sometimes his judgment strikes me as idiosyncratic. For example, echoing the poet and Catholic convert Gerard Manley Hopkins, he writes: "Flaws, loose ends, and rough approximations are what evil cannot endure. This is one reason why it has an affinity with the bureaucratic mind. Goodness, by contrast, is in love with the dappled, unfinished nature of things." So tidiness is a mark of the beast? Goodness is leaving the washing-up?

Shakier, however, is his distinction between evil and wickedness. If evil is the pursuit of nothingness for nothingness's sake, then, he argues, it is not often found so is not something we should lose too much sleep over. Hitler makes the grade, possibly, but Stalin or Mao were merely wicked, for the nothingness to which they reduced their enemies was collateral damage in their pursuit of a noble purpose, the revolution. Eagleton does not argue they are any less culpable for being "merely" wicked  on the contrary  but by such a stringent definition, isn't the book's dedicatee, Henry Kissinger, for Eagleton the embodiment of evil, himself merely wicked?

Richard Coles is vicar of St Paul's Church, Kensington.