Conversion is literally a kind of turn; the convert turns from an old life to a new one. But this about-face can have momentous consequences. It divides life sharply into a before and an after. The past is all regret, the future “the promise of things hoped for.” In “Ash Wednesday,” the great poem of his conversion, published in 1930, three years after he had formally entered the Church of England, T.S. Eliot plays on this notion with sly finesse:

Because I do not hope to turn again
Because I do not hope
Because I do not hope to turn

“Conversion” is also a figure in classical rhetoric, as Eliot knew. In rhetoric, conversion or “transposition” involves the repetition of a word in contrasting senses. In these opening lines, Eliot employed the device not only to announce his own turn of heart but to re-enact it. If the lines are broken, that’s because they reflect all the hesitancy, the second thoughts, the doubts, which riddle the moment of decision; they are lines in which reluctance is set to music.

In “T. S. Eliot” (Oxford, 202 pages, $21), Craig Raine, the English poet, critic, and editor of the literary magazine Areté, devotes some 15 pages to “Ash Wednesday,” which he calls “Eliot’s most difficult poem.” Though he illumines many individual passages splendidly, readers may find the poem more difficult after his analysis than before. Awareness of ambivalence isn’t part of Mr. Raine’s critical arsenal; he’s convinced that Eliot’s work can best be understood as an expression of “the buried life,” a point he presses insistently. To prove this questionable thesis, he engages in relentless exegesis of Eliot’s corpus; only “Old Possum’s Book of Practical Cats” is spared. The effect is of a kind of critical flensing, in which poem after poem is reduced to oil and ambergris. The explications are accompanied by swarming references to everyone from Nabokov (who hated Eliot) to Chekhov, Beckett, Joyce, and Hemingway; these names demonstrate Mr. Raine’s enviably wide reading, if little else. Such close explication will be useful — and often provocative — for those who know their Eliot; for first-time readers, it may be off-putting. Too often “Old Possum” ends up looking like roadkill.

Despite his formidable attention to detail, Mr. Raine occasionally misses the point. Eliot took the opening lines of “Ash Wednesday” from the medieval Italian poet, and friend of Dante, Guido Cavalcanti, but Mr. Raine considers this mere “recondite knowledge,” something “dear to the academic mind.” Yet he fails to mention that Eliot alters Cavalcanti’s line decisively. The Italian poet had written “Because I do not hope to return again.” By changing this to “turn,” Eliot gave the line a peculiar twist with a new significance. For Mr. Raine, the lines represent a “thrice-repeated cry of despair.” But Eliot uses the word “hope” in more than one sense; it hovers between hope and expectation, as do the lines that follow. (Later, as if to gloss these lines, Eliot would state in “Four Quartets” that “hope would be hope for the wrong thing.” Hope, in Eliot’s poetry, can be as hazardous as despair.) “Ash Wednesday” is about the moment of the turn, the moment in which conflicting emotions — regret and hope, faith and doubt, submission and defiance — coexist in musical suspension.

The stumbling block for many readers of Eliot lies in his explicit, and doctrinaire, Christian faith; his work can’t be confronted apart from it. Mr. Raine grapples with Eliot’s Christianity without always understanding it. He claims that Eliot holds at times “unusual, unorthodox beliefs” and gives “rebirth” as an instance; he seems unaware that the notion of rebirth underlies the sacrament of baptism — has he never heard of “born-again” believers? — and confuses it with reincarnation. Again, in a discussion of ghosts in Eliot, he neglects any mention of “the communion of the saints,” a cardinal doctrine which gives transcendent presence to Eliot’s assorted spectres. Mr. Raine says that neither Eliot nor Pascal was a mystic. But Pascal experienced what he called a “night of fire” and wore the tattered memorial of it on a cord around his neck until he died, and Eliot’s poems are irradiated by instants of supernatural vision.

In a controversial appendix, Mr. Raine bravely confronts the persistent accusations of anti-Semitism. Eliot himself declared, “I am not an anti-Semite and never have been.” Though inconclusive, Mr. Raine’s is probably the strongest defense yet mounted; he’s especially good at exposing the bad faith and inconsistencies of certain of Eliot’s accusers. But his interpretations of several notorious passages, while clever, aren’t entirely convincing.

Mr. Raine doesn’t mention the possibility that the young Eliot may well have shared the worst prejudices of his time and place — it would have been unusual if he hadn’t — only to overcome them as he matured and saw, with horror, where they led. Perhaps his letters, if ever fully published, will tell us. That would be the right hope and the best turn of all.

eormsby@nysun.com