The theme comes from a relatively obscure Partita in B flat that Haydn wrote for the Esterházy wind band, and Brahms must have realised at a glance that the Chorale would make an ideal basis for a set of variations, with its clear-cut melody and harmony, combined with the unusual rhythmic structure. The first part is made up of two five-bar phrases and is repeated, then follow two phrases each of four bars and finally a return to the five-bar motif foreshortened by an overlapping cadence which is extended in all for seven bars, the whole of this second section also being repeated.

Brahms based his orchestral version of the theme on the original scoring, but substituting a contrabassoon for the obsolete serpent, and augmenting the brass to four horns and two trumpets. Violins, violas, and timpani are held in reserve until the first variation, where one of the two flutes changes to a piccolo.

For each variation, one particular feature of the original theme is taken up for exploration and development. The first variation picks up the last B flats and over these weaves ornamental patterns; the second takes the first three notes of the theme and makes them stand alone.

With each new variation the emotional feeling and general sound of the music changes. The third variation is recognisable as a version of the first theme in its entirety but the rhythm is now regular and the musical sentences long and sighing.  The fourth seems to be a minor melody built on the four downward notes of the second and third bars of the theme. The fifth is a scherzo-like variation built mainly on the inversion of the first bar of the theme.

The sixth is clearly enough the theme again, now scored for horns and with a rollicking rhythm that calls to mind the hunt. This is followed by a gracious and lively Siciliano, marked graziosi, in 6/8 time. Here the first six notes of the theme are abandoned in favour of an arpeggio figure tapering off into dotted phrases resembling the corresponding measures in the theme. The eighth variation is a tremulous version of the theme with hushed accompaniment.

In the finale the theme is repeated again in seventeen quasi variations, all above a fixed bass of five bars derived from the original melody and bass taken together. The eighteenth statement returns to the original theme and the finale ends with rushing scale passages.