If, following the Council, Gregorian chant is the Catholic Church’s most authentic form of music, then Hummel’s organ music is particularly shaped by this idea — here, one of his answers quoted above applies once again: Gregorian chant is indispensable as a source of inspiration for all genuine church music. After Gregorian chant, the hymn is the next source of inspiration. When he is not using direct passages or fragments from Gregorian chant or hymns, Hummel invents modes as building blocks, which are sequences of notes modified from memory or from models and with which one can work contrapuntally and harmonically.
This working method can be seen and heard particularly clearly in the short pieces he wrote for the ‘Augsburger Orgelbuch für den gottesdienstlichen Gebrauch’ (Four volumes published by Böhm & Sohn, Augsburg). These are: a Prelude in D minor (Book 2), an improvisation: ‘Komm, Schöpfer Geist’ (GL No. 245) (Book 3) and a Postlude: ‘Laßt uns erfreuen herzlich sehr’ (GL No. 585) (Book 4).

In the prelude, a six-note sequence in all possible variations runs through the entire piece. Although one cannot speak of a half-twelve-tone row, it is nevertheless interesting in this context that Hummel rarely employs strict twelve-tone compositional technique, as he wishes to determine his own parameters for composition.

(from Franz A. Stein, “Die Kirchenmusik Bertold Hummels”, Tutzing, 1998)