Bach biographers don’t have it easy. Has there ever been a composer who wrote so much extraordinary music and left so little documentation of his personal life?

Life-writing abhors a vacuum, and experts have indulged in all manner of speculation, generally mirroring their own approaches to the world, about how Bach must have understood himself and his works.

The current fancy is that Bach was a forward-looking, quasi-scientific thinker who had little or no genuine interest in traditional religion. “Bach’s Dialogue With Modernity,” one recent, indicative book is called. In arriving at this view, scholars have ignored, underestimated or misinterpreted a rich source of evidence: Bach’s personal three-volume Study Bible, extensively marked with his own notations. A proper assessment of this document renders absurd any notion that Bach was a progressivist or a secularist.

Bach’s copy of these tomes — which were published in 1681-82 with commentary culled by Abraham Calov from Martin Luther’s sermons and other writings — was unexpectedly discovered in the 1930s among the belongings of a German immigrant family in Frankenmuth, Mich., and is housed today at Concordia Seminary Library in St. Louis. An enterprising publisher in the Netherlands, the Uitgeverij Van Wijnen, has now issued a spectacular facsimile.