As Luca Guglielmi reflected in his program notes for this recital, cast in his familiar first-person tone, “The dates in the titles of each half of this program simply suggest an occasion, the actual dates of composition of each piece preceding or following the date given.” A confabulation of two putative Dresden recitals by Bach, derived fancifully but plausibly from historical happenings, is an excellent point of departure for the flight of association Signor Guglielmi proposed to his Boston Early Music Festival listeners,  which included greater Boston’s seasoned historic keyboard public, a hefty dollop of the core BEMF audience, and a good admixture of other visibly engaged music lovers. All were clearly drawn to Back Bay’s First Lutheran Church on Friday by the dual appeal of hearing this prominent Italian master and taking in a serious dose of Bach.

If I may paraphrase the original of a sour appraisal by Johann Adolf Scheibe (Hamburg, 1737), with its odor of lack of penetration rather than of musical acumen:

Bach’s music is bothersome, for it is unnatural, artificial, and in a confusing style. Instead of leaving decoration to the performer, he writes out the ornamentation, which obscures the beauty of the melodies and harmonies. He fashions a dense polyphonic setting that equates each voice with the others, rather than merely accompanying a tune. It’s just too complicated. The music sounds overblown and unnatural, even oppressive, instead of trying for natural simplicity.

Guglielmi feels that Bach must have fired off a warm riposte to this published critique, celebrated in its time. In the light of the centuries since, it is apparent that, early on in his tenure at the Thomaskirche, from 1723, the composer took special pains to manifest a broad and masterly variety of styles, small- and large-scale polyphony certainly among them.

Especially in such personal statements as his Partita No. 2 in c, S.997 (late 1720s), Bach extended himself in any stylistic direction that served his affective and æsthetic aims. Guglielmi’s performance Saturday, on Peter Sykes’s gloriously refurbished French double (D. Jacques Way, 1984, after Jean-Henri Hemsch, Paris), drew dark songfulness from each of the four extensive movements. The plangent growl of this, one of Boston’s finest modern-day cembali, and the performer’s quiet delight in singing sonority, made for an opener of the sort listeners dream of hearing. Peeking through a solid, earthily steady overall pace in each movement were carefully judged but spontaneous-feeling details of jeweled clarity. Too, the minute push and pull of masterfully implemented rubato within small phrases put a spring in the Bachian step, a willowiness that caused line and gesture to glow within the fine groundedness of the great tonal arches of the writing. I must single out the burnished, spare, patrician unfolding of the very lovely Sarabande, in which an overall fantasia-like freedom lived within Guglielmi’s secure and metrical forward thrust. This suite was an ear-opener on a rare, high level.

The Italian Concerto S.971, may have been overplayed for decades, but there’s good reason. Guglielmi demonstrated why, bringing out that exquisite mix of virtuosity and joyous affect that pervade its every bar, in a gripping performance. It was sonorous to a genuinely unfamiliar degree, thanks to his lyrical sustaining of phrases and lines. Only with a harpsichord of exceptional quality can even the best player elicit such organ-like resonance. The instrument had just been restrung, re-quilled, and voiced, with arresting results. The subtlety of the voicing allowed the usual play between manuals I, II, and their coupled resources to rise to a height I had not experienced even on the best surviving German originals.

In the Chromatic Fantasy and Fuge in D Minor, S.903, his concluding cembalo work, Guglielmi applied note velocity, as of course the piece requires, but in the service of an estuarine wash of harmonic polychrome. Once more, his special way with sustained sound, held-out strands of musical line, assured that the welter of flitting arpeggiations added up to harmonically straightforward simplicity. When, as so often in this work, individual notes and skeins of phrasing stood still amid the surging waves, the remarkable ability of this particular clavecin français to sing on made strong painterly detail of them, not naked, thin pauses teetering between the tidal washes of fast tutti passages. Guglielmi’s supreme clarity of gesture throughout the Fantasy continued through the Fugue, a bravura architectonic building-up with its explosive, then suddenly subsiding end.

The scores in the harpsichord part of the recital were straightforward posits of what Bach, visiting from Leipzig, might have played in Dresden’s Palais Keyserlingk, where harpsichordist-organist Joh. Gottlieb Goldberg — he of the Variations — worked for St. Petersburg’s envoy to the Saxon court. The program Guglielmi chose to illustrate what Bach the performer might have assembled on the music desk of Gottfried Silbermann’s famous three-manual organ (1736) in the nearby Frauenkirche was dramatically more fanciful. He opened with a tripartite Prelude, Trio and Fuge in C “per il Padre Martini di Bologna” that relied little on the pedal. The prelude was the first piece in the Well-Tempered Clavier II, then came the familiar a-minor second movement of the organ Trio Sonata No. 5 in C Major, S.529. How pleasant to hear the first fugue in WTC I deliciously unsettle the inner ear’s long-sanctified context for this short fugue, familiar from endless auditions on percussive keyboards. Once again, this player’s singing, joyous elicitation of sound and line lent wings to what could well have been pedestrian.

I now must take issue, not with the excellent pacing Guglielmi brought to the three movements of the Organ Piece in G Major, S.572, a unicum among of the composer’s keyboard opus, but with his slightly hard-edged registration. As with the harpsichord playing, he went for dark and rich rather than brilliance. So far so good. But the big 8’ trumpet on the Great, with reticent support by lower-pitched flues, simply did not carry the movement along in a way I found credible. Some who were there may not agree. Few organists could have pulled this feat off with such astonishing clarity of touch and phrasing, but so full a registration didn’t win the argument. The fully registered Gravement worked better, though hearing so much gleaming detail within its glacially forward-moving mass was not to my taste. The closing Lentement was cast in the same registrational trappings as the opening, eminently successfully, with that superb Central German trumpet underpinned with a savory mélange of, once more, foundation-oriented flues.

Bach adored odd musical gesture. There are no stranger and more delightful examples of his quirky, at times edgy humor and tongue-in-cheek skewing of his era’s norms than his four organ Duets, S.802-805. The special nature of First Lutheran’s popular Richards, Fowkes organ, mostly finished in 2000 and completed with superb reeds in 2011, is now different from when the instrument was new. These final stops added brilliance, weight, and color to the organ’s already diverse timbral arsenal, into which Guglielmi dipped with relish. The warmth and visceral conviction with which he plays put across the biting, lyrical, or angular characteristics of each duet in as convincing a manner as I’ve heard. The pieces are viable harpsichord music, but the organ brings them out to better effect. Some years ago, I heard this idiosyncratic quartet of works stunningly played on a fine Dutch copy of a 1740s Silbermann Flügel, the Saxon intermediate stage between Cristofori and the Viennese school; this approach, historically justified in view of Bach’s familiarity with the Silbermann pianos, may have been just as persuasive as what Guglielmi did, but he had the advantage of that much more color and sharp-edged registrational resources to highlight the wayward, “go stand in the corner!” impishness of the duets. Additionally, he draped them in a grandeur I had never before heard. Utter, shivering pleasure throughout.

The formal part of our memorable evening closed with the masterful Prelude & Fugue in A minor, S.543, a great jewel in the Bach crown. The very full registration, just darker than the usual tutti, suited the propulsive, sinewy musculature of this exceptional musical architecture. So profound a score is ill-served by hectic virtuosity, and Guglielmi permitted the long lines to extend and extend, like cords in a thoroughbred’s gleaming neck. His encore, Liebster Jesu, wir sind hier, S.731, from the miscellaneous organ chorales — there are two other settings — was as glowing as the previous work had been monumental. A simply perfect evening.

Veteran recording engineer Christopher Greenleaf collaborates with chamber, early, and keyboard musicians in natural acoustic venues on both sides of the Atlantic. He is active as a writer, translator, photographer, and acoustic consultant.