The music of Johann Sebastian Bach (1685–1750) gives us a unique earful of divine glory and omnipotence. Whether the mighty “Saint Matthew Passion,” the poignant “Goldberg Variations,” or the mystical “Musical Offering,” Bach’s works retain their essential mystery and surprise. The more we listen to Bach, it seems the less we know about him. The familiar “Toccata and Fugue in D minor” for organ fervently played by everyone from the Phantom of the Opera to Erich von Stroheim in “Sunset Boulevard,” turns out not to be by Bach after all. Such is the conclusion of Peter Williams, a professor emeritus of musicology at Duke University and the University of Edinburgh, in his authoritative new “J.S. Bach: A Life in Music” (Cambridge University Press, 405 pages, $24.99).

In Bach’s cantatas, some choruses are memorable for the thrill of massed voices in modern-day performance. Yet they were likely originally written for a single voice per part, making a vocal quartet the full measure of sonority in many cases. Such was the theory advanced by an American musicologist and conductor, Joshua Rifkin, and seconded by Martin Geck in his massive 2000 study, “Johann Sebastian Bach: Life and Work,” now newly translated from the German by John Hargraves (Harcourt, 738 pages, $40). Mr. Geck, who teaches at the University of Dortmund, has produced a discursive, leisurely march through Bach’s oeuvre that benefits from the skills of Hargraves, an experienced literary translator of Elias Canetti and Günter Grass. Mr. Geck’s book is a curiously helical construction that begins with information about Bach’s early biographers, then shifts into what is grandly called “The Stations of Bach’s Life,” before addressing in separate sections his vocal and instrumental music, and their repercussions. By contrast, Mr. Williams’s book is more thorough — composed and relatively concise, with life and music integrated into the narrative. Yet Mr. Williams’s prose style is humdrum, with an occasional baroque flight, such as a sentence in four languages which describes Book Two of the “Well Tempered Clavier” as a “harpsichordist’s vade mecum, surveying styles from strict counterpoint in the stile antico to the various galanteries à la Dresde.”

On a human level, Mr. Williams’s approach to Bach can be excessively fastidious. Discussing a bill Bach ran up for beer, Moselle wine, and brandy, Mr. Williams states that it “represents, one must hope, consumption over several days and by several people.” Why should we hope Bach never got smashed after a hard day sweating over “The Art of Fugue” or some other masterpiece? Bach’s sensual appetites are not in question; he did father 20 children, after all. Bach’s bellicose tendencies, including street brawling and repeated squabbling with employers, are given a “positive interpretation” by Mr. Williams: “Whatever hindered his creative duty would not be tolerated.” Yet surely Bach needs no apologia. My friend the French writer Emil Cioran used to say, “If anyone owes everything to Bach, it’s God. Without Bach, God would be a thirdrate character.”

Depicting a saintly Bach whose every action can be justified misses the compelling paradox of a very human composer who managed to create the “St. Matthew Passion,” among the most convincing devotional music ever written. Mr. Geck’s book is betterrounded, including a plausible discussion of the anti-Semitism in Bach’s “St. John Passion” oratorio, which includes choruses by rapacious Jews who are depicted as enemies of Jesus, repeatedly demanding his crucifixion. As the quintessential Lutheran composer, Bach was likely influenced by Martin Luther’s savagely sarcastic tract “The Jews and Their Lies (1543)” which was disavowed only in 1994 by America’s Lutheran church. Bach was also no fan of “Turks and Popes,” as he makes plain in the text of his Cantata BWV 18. (BWV, or Bach-Werke-Verzeichnis — Bach Works Catalogue — is the universal system used to catalog Bach’s music, although the unhelpful index of Mr. Williams’ book is mistaken in assuming that average readers will know these BWV numbers by heart).

Whether or not the man was as perfect as his music, the latter can be unbearably moving, as when the Evangelist in the “St. Matthew Passion” narrates the episode of Peter’s Denial of Christ: “Und ging heraus und weinete bitterlich” (And he went out, and wept bitterly). As sung by the British tenor Peter Pears on a Decca recording conducted by Karl Münchinger, this passage expresses a world of remorse. In the same oratorio, the chorale “Wenn ich einmal soll scheiden” (“Should I at some time depart”) is sung after Jesus’s death, and a 1954 version with a primal abandonment to grief is led by Wilhelm Furtwängler, reprinted on EMI. Yet Bach’s most stunning works may be those expressing undiluted joy.

There is rational frenzy in the “Ciaconna” for violin solo as performed with laserlike accuracy by the Belgian violinist Arthur Grumiaux on Philips Records. Or the exuberance of Cantata BWV 30, “Freue dich, erlöste Schar” (Rejoice, O ransomed throng), as led by the great choral conductor Blanche Moyse of Brattleboro. Her magnificent 1970s performance, one of the finest of the entire Bach discography, is available on CD from the Brattleboro Music Center (www.bmcvt.org). The much lauded series of cantatas conducted by Nikolaus Harnoncourt and Gustav Leonhardt on Teldec include “Der Himmel lacht!,” (The Heavens Laugh) BWV 31 featuring the exalted soaring of boy soprano voices, and the cantata movement “Nun ist das Heil und die Kraft” (Now is the health and the strength) BWV 50, has irrefutable geometric grandeur.

Peter Williams aptly concludes his astute new volume by stating that Bach’s achievement is a “mystery.” Using the Merriam-Webster definition of “mystery” as a “religious truth that one can know only by revelation and cannot fully understand,” this is literally true.

Mr. Ivry last wrote for these pages on Polish literature.