In this comprehensive study of Olivier Messiaens magnum opus, Saint François dAssise, Vincent Perez Benitez examines the opera from both theological and musical-analytical perspectives to ask how Messiaen expresses his Catholic theology through his work. Benitez combines a close reading of the opera score with accounts from Messiaens associates, studies of Messiaens birdsong notebooks and other primary documents, and an examination of the religious, musical, poetic, and visual arts literature with which the composer was familiar to explore how the operas harmonic language and sound-color relationships motivate its musical meaning and expression. Through his analysis of these diverse sources and comparisons of Saint François dAssise with other works such as Bergs Wozzeck and Wagners Parsifal, Benitez places Messiaens compositional practice within larger musical perspectives and historical contexts.