For the anniversary of the chancel organ, the choristers and adult singers will present Vierne’s expansive mass for choir and two organs, a performing circumstance rarely used because of the practicality of a church having two full organs in its sanctuary.

“In 1899, Vierne set the Latin text of the mass ordinary without the Credo, which makes it a formally a short mass or missa brevis. He imagined a mass for orchestra, but Charles-Marie Widor, his teacher and organist at Saint-Sulpice in Paris advised him to employ organs, for practical reasons. The mass was first performed at Saint-Sulpice in 1901, on the Feast of the Immaculate Conception, 8 December. The church has a great organ (grand orgue) in its back built by François-Henri Clicquot which Aristide Cavaillé-Coll had reconstructed and improved in 1862. The choir organ, in the choir, was built by Cavaillé-Coll in 1858. Vierne planned the effect of sound from the far ends of the church. In the premiere, Widor played the main organ, while the composer, who was by then organist at Notre-Dame de Paris, played the choir organ.”
—Wikipedia