Many have proved invincibly, from the sentiments of the Fathers - among others: St. Augustine, St. Ephrem, St. Cyril of Jerusalem, St. Germanus of Conantinople, St. John Damascene, St. Anselm, St. Bernard, St. Bernardine, St. Thomas, and St. Bonaventure - that devotion to Our Most Blessed Virgin is necessary for salvation, and that it is an infallible mark of reprobation to have no esteem or love for the Holy Virgin while, on the other hand, it is an infallible mark of predestination to be entirely and truly devoted to her.
St. Louis Marie de Montfort
Further reading
This excerpt gives a concentrated statement of Montfort’s conviction about devotion to Mary. His True Devotion to Mary develops that conviction within a fuller account of consecration to Jesus through Mary and the practices that accompany it.