The »Twenty-four Pieces pour Orgue« of Joseph Callaerts is an answer to Guilmant‘s »Pièces dans différents styles« in a way. These pieces are beautifull and interesting as well as every French collection of organ music (Boellmann, Dubois, Gigout, Rousseau, Salomé etc.).
Joseph Callaerts was rich enough to earn not money with his profession. He was after some other engagements organist of the Antwerpen cathedral (Belgium). Here he got a large symphonic organ from Pierre Schyven which is preserved until today.
As far as I know:
Nobody has understood the high importance of Callerts for the history of organ music. I have never seen an a organ-composer who adapted the style of Richard Wagner to the organ in such an unique way.
One will find in all this pieces details from Wagner‘s music: melodies, harmonic passages, or themes. Callaerts didn‘t learn this musical features from his teacher Lemmens. His promotion of the Wagner style seems to be his own idea.The key for understanding the intentions of Callaerts is the Toccata in D major - you will see.