In 1936, attempting to overcome his reputation for musical flippancy, Poulenc began studying the motets of Montverdi, with Nadia Boulanger. Around the same time, his close friend and contemporary, Pierre Octave Ferroud, had died. Amidst this personal crisis, Poulenc was led back to the Catholicism of his youth and this confluence of spiritual and musical interests led him to compose the Messe en Sol Majeur (Mass in G). Available here is the vocal score for SATB Choir a cappella.