In 1955, a young man from Canada stood the classical music world on its ear. Glenn Gould’s recording of Bach harpsichord music on a modern piano was one of the most significant musical events of the second half of the 20th century. It opened up the entire period-instrument debate and redefined what it meant to be faithful to the original score.

Gould’s record of the Goldberg Variations is an undeniable classic, but it is not Bach. The piece, written so that Bach’s pupil Johann Gottlieb Goldberg could attempt to cure the insomnia of the Russian ambassador to the court of Dresden, Count Kayserling, was fashioned for a two-manual harpsichord, an instrument with plucked rather than hammered strings. Its sonorities and timbre are entirely different from that of the piano, its soporific value questionable. As Gould wrote in his notes, “if the treatment was a success we are left with some doubt as to the authenticity of Master Goldberg’s rendition of this incisive and piquant score.”

On Wednesday evening at Saint Bartholomew’s Church, Matthew Dirst performed the work in its original form. The differences between harpsichord and piano became clear immediately, when Mr. Dirst announced that there would be an intermission after Variation XV. This was not so much to give the audience a break, but rather to retune his instrument.

Mr. Dirst is an associate professor at the University of Houston and the organist at St. Philip Presbyterian Church. He is the founder and artistic adviser of Ars Lyrica Houston, an ensemble that presents rare Baroque works. In 2003, they mounted the American premiere of Handel’s first oratorio, “Il Trionfo del Tempo e della Verita,” in a dramatized version.

The Goldberg Variations are based on the bass line of a sarabande from the Notebook of Anna Magdalena Bach. Bach jettisons the rhythm of the dance even before the end of the opening statement, establishing a more measured and stately pace.

Mr. Dirst presented this fertile theme in an unhurried manner, allowing its broad rhythmic pattern to unfold slowly, presenting the source material for the audience to examine before the artistry of the composer held sway.These variations are extremely difficult to communicate properly, and Mr. Dirst certainly expended a noble effort in their service.

In Variation I, a polonaise, the harpsichordist replicated the original tempo of the Aria opening in the left hand, but created an aural illusion with his florid treatment of the melody in the right. The sheer number of notes on top created the impression that he was actually playing faster than his initial utterance. It was the triumph of the florid over the grounded.

Variation III begins the cylindrical blueprint of the piece, a monumental drafting of musical architecture wherein canons on the individual notes of the scale provide the loadbearing columns for the superstructure. These canons, from the unison through the ninth, give the otherwise motley material a tight cohesion.

Mr. Dirst proved himself to be an interesting colorist, providing kaleidoscopic variety as the evening developed. His Variation IV was a passepied of decidedly askew rhythmic values; his insistently monochromatic Variation V produced much headbanging among the audience members.

Variation VII was a spirited saltarello, XIII a beautiful and lingering cantilena. In XIV, Mr. Dirst exhibited the finest playing of the night: This was an extremely taut and accurate traversal of an arabesque with a propulsive, almost primitive, sense of meter.Variation XIX is a minuet with much more of a plucked quality than can be reproduced at a modern piano, and Mr. Dirst demonstrated just the right spidery touch for this contrasting bit of color.

Only three variations – XV, XXI, and XXV – are written in the minor. Mr. Dirst presented the second of these as an intense, highly dramatic foray into darkness. Strangely, though, some in the audience had gone the way of Count Kayserling and were not in a state to be rattled.

Variation XXII should be granitic, magisterial,seeking the triune like earlier Italian choral music, but Mr. Dirst apparently hears it differently. His fast tempo seemed misguided here, but he is the Bach scholar, not me.

All ends humorously: Variation XXX is a quodlibet, a satirical style featuring two popular songs – one titled “Cabbages and Beets Have Driven Me Away.” And finally, a simple statement of the original air, totally transformed in our mind’s ear because we have shared its journey. Mr. Dirst introduced it as an old friend.