If, following the Council, Gregorian chant is considered 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 postlude “Let us rejoice with all our hearts” ( GL No. 585), the two melodic sections of the hymn are used verbatim on different pitches, expanded in a hymnal and rhythmic manner in keeping with an Easter postlude. The whole is enlivened by a five-note figure, used ostinato in the upper voice and bass, which suggests the “Alleluia ”. A simple prime example of liturgical organ playing, which could also be used as a teaching example.

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