Simply put, consider this a fugue where the tension progressively builds as it advances. While this is not uncommon in Bach's works, the technique employing inversion is truly remarkable.

The piece commences with the original subject. This spans from measure 1 to the second beat of measure 4. Subsequently, the subject appears successively in each voice, as is customary.

Beyond measure 30, the original subject then appears in stretto. This stretto occurs from the first beat of the soprano in measure 33 and the second beat of the bass.

From measure 52, the inversion of the subject is introduced. This is a version where the subject is inverted, as if reflected in a mirror. From measure 67, a stretto of this inversion takes place. In measure 67, this stretto begins from the second beat of the soprano and the first beat of the tenor.

By measure 80, the original and inverted subjects appear in stretto. This occurs from the first beat of the soprano and the second beat of the tenor in measure 80. At this juncture, the tension significantly escalates. Subsequently, another stretto of the original and inverted subjects occurs in measure 89 (in the alto and bass), and finally, in measure 96, all four voices simultaneously present the original and inverted subjects in stretto, culminating dramatically with a Picardy third – an extraordinary fugue.