In the AHJ, Vol. 13, No. 1. Summer 1991 there is an article by Kathy Bundock Moore, Marcel Grandjany: A Centennial Biography. This includes a short analysis of his composition style, grouping the solo pieces as his early period of composition. She lists Rhapsodie, Op. 10 as 1921. Significant events would include him giving up the harp during WWI (1914-1918), “He was disappointed at his inability to serve on active duty and stopped playing the harp out of respect for those fellow musicians who had been called to the front lines–the list of those who died or were maimed is long indeed.” (p. 5) He was then married to Georgette Boulanger in 1919. It appears that otherwise he was teaching, and “In 1921, he was asked to begin a harp class at the opening season of the Conservatoire Americain at Fontainebleau (a tremendous honor for him), joining such well-known instructors as Nadia Boulanger, Paul Vidal…, and organist/composer Charles-Marie Widor.”
>Rhapsodie pour la harpe, Opus 10 (1923) by Marcel Grandjany (1891-1975) The Rhapsodie marked Grandjany’s debut as a composer of solo works of symphonic conception. Its intended use was as a recital opener to “impose the harp,” as his teacher Renié, to whom the work is dedicated, had advocated. The theme of the Rhapsodie is based on a Gregorian chant (Salve Festa Dies) which is sung at the conclusion of the Easter Vigil for the newly baptized. To a devout Roman Catholic, this melody has enormous emotional significance – it is Grandjany’s love song to his Mother Church, but as with all of his compositions, it transcends traditional music for the harp and reaches, through its large design, emotional input, and appropriate technical challenges, another plane rarely visited in our repertoire.
and there’s a great deal more info available, too.