Christians, Muslims and Jesus. By Mona Siddiqui. Yale University Press; 285 pages; $32.50 and £20. Buy from Amazon.com, Amazon.co.uk

RELIGION is a tricky subject for scholarship. Even the most professional academic is bound to have personal feelings about the faith under scrutiny. Some see this as cause for concern. Indeed Reza Aslan, one of America’s best-known writers on religion, recently came under fire for his new book about Jesus (“Zealot”, reviewed in the July 27th issue of The Economist). Because he is a Muslim who once embraced Christianity and then dropped it, Lauren Green of Fox News accused him of writing with a “clear bias”. No, Mr Aslan replied, he was writing as a scholar. His response was articulate and dignified, and the interview has helped sell quite a few books, but it will hardly sway those who believe Mr Aslan is writing with a Muslim agenda.

Mona Siddiqui, a professor at Edinburgh University’s school of divinity, makes no secret of the various strains of thought that inform her study of Christians, Muslims and Jesus. Parts of her book are rigorously academic and arcane, other parts are very personal. Unlike Mr Aslan, she does not confine her meditations on her own faith to an introduction. Rather, she ambitiously weaves her personal and scholarly views throughout.

She presents certain basic facts: Muslims revere Jesus as a uniquely inspired prophet who was born of the Virgin Mary, ascended to heaven and will come again. Yet Muslims cannot accept that Jesus was the son of God. This, they believe, reflects a flawed view of both Jesus and God. As Ms Siddiqui shows, Christians and Muslims sparred with one another intensely during the early centuries after Islam’s rise, with each side vying to be the ultimate revelation of God. But the two faiths did at least grudgingly acknowledge one another as monotheistic, despite Islam’s firm rejection of the Christian view of God as a trinity: Father, Son and Holy Spirit.

The most compelling passages are the personal ones, in which the author sets out some of her own dilemmas. A Muslim, she describes herself as fascinated by Christianity. But she remains committed to an Islamic belief in a God who is utterly transcendent and so could not have taken human form, as Christians say of Jesus.

She writes with clarity and empathy about the core doctrines of Christianity (as expressed by both the church fathers and her own Christian friends). But unlike other comparative-religion scholars, she does not paper over the differences between these two global monotheisms. The crucifixion of Christ is an event of cosmic significance in Christianity, but it has no such place in Islam. Muslims reject the idea that a God-man was martyred for human sinfulness; Jesus’s death is an enigma in Islam and his crucifixion deemed an illusion.

To her credit, Ms Siddiqui perceives the dilemmas faced by the early Christian church better than many contemporary liberal Christians do. After all, she shares with the church fathers an uncompromisingly God-centred view of the world—one that is foreign to most modern Westerners, even those who practise a religion. She senses why the idea of God becoming man seemed to the church fathers to be at once outrageous and also true.

Still, however deep her intuitive connection with Christianity, she ends the book by pinpointing why she is unable to accept the Christian understanding of God. She cannot submit to the idea that humanity was estranged from God before Jesus came; or that as Jesus God walked on earth and made a supreme sacrifice (the crucifixion), which somehow ended that estrangement. For her the Christian deity is both too far away and too close.

That is a personal choice, not an intellectual position. But some readers may conclude that Ms Siddiqui’s study of the Christian church fathers, diligent as it is, falls short. It is true that Augustine, a pioneer of Christian thought, stressed man’s alienation from God before Jesus. It is also true that in the last millennium or so the idea of Christ’s death as a necessary sacrifice has been stressed by Catholic and Protestant teaching. But there have always been Christian thinkers who feel that Augustine exaggerated human sinfulness. Plenty more reject the view that the crucifixion was a way of assuaging an angry God. Ms Siddiqui’s dialogue with Christianity will get even more interesting if she engages with the many Christians who agree that Augustine’s God is too remote.

In any case, both Christians and Muslims will always wrestle with the paradox of God’s distance and proximity. The God of the Koran, for all his utter transcendence, is “closer to man than his jugular vein”, whereas Saint Paul told the Athenians of a “Lord of heaven and earth who does not live in temples, yet…is not far from any one of us.”