The "15 Pièces sur des thèmes liturgiques" were composed for organ or harmonium, so, if you are going to have a go at these, you need to "figure out what notes you will play and those that you won't," since the organ "version" will be a lot different than the harmonium one.
All of these pieces are designed to serve a liturgical function, as they would all be played during the Mass. They aren't "concert works," although they are not short of beauty.
Albert Paul Alain was born in 1880 in Saint-Germain-en-Laye, and lived and worked there for most of his life. He was organist of l’église de Saint-Germain-en-Laye, a postiton he held until his death in 1971. He was the father of Jehan and Marie Claire.