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.

All three volumes are inscribed “JSBach.1733” and contain a host of handwritten corrections and comments. Bach handwriting experts have identified the vast majority of these verbal entries as “definitely Bach” or “probably Bach.” Hundreds of passages are further scrawled with marginal dashes and other nonverbal markings. Although these are harder to evaluate, physicists at the Crocker Nuclear Laboratory have concluded through ink analysis that “with high probability, Bach was also responsible for the underlinings and marginal marks.”

Where does all this science get us? Bach’s notations bear witness to a life of conservative Lutheran observance.

Within Calov’s scripture verses, there are many small printing errors that would doubtless go undetected by even the most biblically literate reader. Yet time and again Bach has restored text that was far from clearly missing, or has changed perfectly plausible sounding, but in fact unattested, wording to the standard Lutheran rendering. None of these corrections stem from the list of errors printed in Calov’s appendix.

Some biblical scholars have concluded from this that Bach acted like an astute textual critic, poring over Calov’s volumes and painstakingly comparing them, line by line, with other Lutheran Bibles. But there’s a simpler and more likely scenario, fully grounded in conservative 18th-century social and religious practices.

Picture the people of Bach’s household on free evenings, gathered in their living room for the activity of reading aloud. The children take turns reciting from a family Bible for practice in reading and elocution, not to mention spiritual edification. The patriarch follows along in his magnificent Study Bible, in part to make sure there’s no passage-skipping from the lectors, and in part to allow him to reach for his inkwell whenever he spots, compared with what he’s just heard, an error in Calov’s scriptural verses.

Tellingly, in something akin to what linguists call a mondegreen, Bach at several passages apparently misconstrued what the children — in this reconstruction of the scene — had said, and emended a scriptural verse’s legitimate Lutheran rendering to a similar-sounding but unattested wording. At Isaiah 16:8, Luther’s text reads: “its vine-branches are scattered, and over the sea.” Bach caught sight of Calov’s obvious typographical error “Fesser,” but he evidently misheard a lector’s utterance of the correct wording, and thus emended Luther’s intended “Feser” (vine-branches) to the biblically unattested “Fäßer” (wine-casks).

The Calov volumes also provide insight into Bach’s professional and personal concerns, showing that he understood himself less as a modern artist than as a preacher who was following his religious vocation. An annotation in Latin that the Crocker Laboratory physicists have filed under “definite Bach entries” makes for especially poignant reading, as it takes note of manifold passages in the Bible’s Solomonic literature speaking of how to find godly solace in a world that is hostile to people faithfully pursuing their divine callings. Sundry administrative records indicate that Bach often fell into trouble over philosophical differences with his employers about the place of music in worship and in education.

Only a handful of Bach’s entries in Calov concern music, and these have received the most extensive — indeed, typically the only — attention from biographers. Leading writers have striven to explain these marginalia as progressive. In truth, all of them straightforwardly reflect conservative Lutheran thinking. What they share as well is a premodern interpretive approach called “typology,” whereby events and principles in the era of ancient Israel act as “types” or “shadows” for their correlated “antitypes” or “substances” in the era of Christianity. Typology was looked upon less as a scholarly path to intellectual understanding than as a doctrinal path to spiritual comfort.

Citing one of Bach’s annotations on music as key progressivist testimony, John Eliot Gardiner, in his 2013 biography “Bach: Music in the Castle of Heaven,” wrote: “Bach understood that the more perfectly a composition is realized, both conceptually and through performance, the more God is immanent in the music. ‘NB,’ he wrote in the margin of his copy of Abraham Calov’s Bible commentary, ‘Where there is devotional music, God with his grace is always present.’ This strikes me as a tenet that many of us as musicians automatically hold and aspire to whenever we meet to play music, regardless of whatever ‘God’ we happen to believe in.”

What a lovely, modern idea! Alas, no aspect of it could possibly have been part of Bach’s understanding.

Lutherans like Bach certainly would have condemned as a grievous sin of idolatry any notion that the essence of a piece of music is, or turns into, the essence of God. And Bach’s somewhat cryptic note is not even about the less heretical notion of God’s possibly just “dwelling” within music, either. Its language plainly echoes more particularized orthodox Lutheran observations about God and music that were laid out in Johann Gerhard’s “School of Piety” (1623), one of many books of practical theology listed in Bach’s estate inventory.

Thus the impetus behind Bach’s remark was not progressivist but doctrinal. The Old Testament text Bach commented on presents the “shadow”: At the sound of the priestly music, the “Glory of the Lord” inhabited the Jerusalem Temple. Bach’s marginal note points to the orthodox Lutheran understanding of the “substance”: At a rendering of devout music, the “Grace-Presence” of God will always inhabit the hearts of Christian believers, whose bodies, according to the New Testament, are “a temple of the Holy Spirit.” Bach had worked with these very tenets earlier in his career, when he composed glorious musical settings of them in his Cantata No. 172, “Ring Out, Ye Songs.”

Beside another significant passage in Calov, Bach wrote, “A splendid demonstration [‘Beweis’] that music has been mandated by God’s spirit.” Christoph Wolff’s magisterial biography, “Johann Sebastian Bach: The Learned Musician” (2000), identifies Bach’s use of “Beweis” here as an approving nod toward the term’s centrality in the progressive methodology of scientific empiricism, a methodology that was held already during Bach’s lifetime to be applicable also to theological principles.

But the noun “Beweis” was also used frequently, from the 16th through 18th centuries, in the same conservative way it’s used in Bach’s note: for the “demonstration” of theological principles through study of biblical revelation alone. Bach’s music likewise employs the word “Beweis” in its conventional pre‑Enlightenment, nonscientific sense. A recitative in his “Christmas Oratorio” proclaims that a believer’s heart should safeguard the biblical account of the miracle of Christ’s birth “as a sure demonstration [‘Beweis’]” of salvation.

Bach was contractually answerable for choosing the liturgical poetry he set to music, and modern-day critics, in a bit of wishful thinking, often proclaim that his theologically conservative choices were designed simply to please his employers. But on this biographical question, the Calov volumes turn out to be acutely instructive. The sentiments expressed in Bach’s vocal music are continually paralleled in his Calov notations. Most of his vocal music was composed from the 1710s to 1730s, whereas his Calov notations were entered in the 1730s and 1740s. In view of the fact that almost all the private notations come well after the public compositions, Bach obviously subscribed to the sentiments expressed in his vocal music.

Both Bach’s music and his Calov notations put powerful stress upon: (1) contempt for human reason, along with the exalting of biblical revelation as the proper arbiter of truth; (2) disparagement of notions of human autonomy and achievement, along with the exalting of dependence on God, including for one’s position in the social hierarchy; (3) contempt — explicit or implicit — for Judaism, Catholicism and Islam, along with the exalting of orthodox Lutheranism; (4) disdain for foreigners, along with the exalting of German faithfulness and goodness; and (5) the emphatic exalting of monarchical power, as authorized not by the people but by God. Nowhere in Bach’s music or Calov notations are these sentiments contradicted.

In short, Bach, in his unswerving religious conservatism, was living and working very much at odds with the progressivist currents of his day, and ours. While we’re arguably free to make use of him and his music in whatever new ways we find fitting, we ought also to be on the ethical alert for casting Bach in our own image.