The importance of the Rosary. Resources: The devotional books about the Blessed Virgin Mary by St. Alphonsus Liguori, St. John Eudes, and St. Louis de Montfort. The Secret of the Rosary by Saint Louis de Montfort. Recommend Devotions: Sacred Heart of Jesus  and the Immaculate Heart of Mary. For a academic coverage about Middle Ages devotion to Our Blessed Mother Mary, I  highly recommend the two books about Mother Mary by Rachel Fulton Brown. Warning: these books ARE NOT light reading!