Bach: Music in the Castle of Heaven by John Eliot Gardiner Knopf, 629 pp., $35.00

One of my most moving encounters with the music of Johann Sebastian Bach took place in the spring of 1997 in New York City’s Central Synagogue. I was there to pay last respects to Gabe Wiener, a talented young recording engineer who died of a brain aneurysm at age twenty-six. I had approached Gabe earlier in the year to see if his recording company, PGM Classics, would consider collaborating with the American Bach Society, which I led at the time, to produce a compact disc of previously unrecorded organ music from Bach’s circle. Gabe enthusiastically agreed to the proposal, and together we embarked on a project we called “The Uncommon Bach.” We had just settled on the repertory and the organ when I received word of his death.

There was great lamenting at the memorial service that this talented young man had been snatched away in the midst of important work, with so much promise unfulfilled. The service began with Gabe’s recording of Salamone Rossi’s Hebrew setting of the Songs of Solomon, a gorgeous yet relatively unknown Venetian masterpiece. It continued with readings from the Torah, eulogies, and the Kaddish. But at the center of the service, at what proved to be the emotional high point, a countertenor sang the Agnus Dei from Bach’s Mass in B Minor.

The Agnus Dei is one of Bach’s last creations, derived from music he had used twice before, in 1725 and 1735, with different texts. He was clearly pleased with the highly effective aria, and in 1749 he refined it a final time for insertion into the concluding portion of the B-Minor Mass. Time was running out. The cataracts that had plagued his eyesight for some time were rapidly advancing, and the Agnus Dei was one of the last pieces he completed before submitting to the eye operations that led to his death. Bach normally expanded music when he revised it for further use, but in this unusual case he shortened the original, distilling its emotional and musical essence and creating a new, intensified version of the piece. He had less than a year to live.

As the singer intoned the ancient Latin text—Agnus Dei, qui tollis peccata mundi, miserere nobis (Lamb of God, who taketh away the sins of the world, have mercy upon us)—enhanced by a poignant unison violin line and anguished pauses, I could not help but marvel at the miracle of hearing this music from the Roman Catholic Latin Mass Ordinary, written by a Lutheran composer in Leipzig, in a Reform Jewish temple in New York City. Afterward I asked Peter Rubinstein, the senior rabbi of Central Synagogue, why he picked this particular work rather than something from the Jewish repertory. “We chose Bach’s Agnus Dei,” he replied, “because it was the right piece,…