The Protestant Reformers broke with the cult of the saints as sharply as they broke with almost anything else in late medieval practice. Luther and Calvin both argued that invoking saints had no scriptural warrant, that it obscured Christ as sole mediator, and that shrines, relics and pilgrimage had become a trade in indulgence and fee rather than piety, an economic complaint as much as a theological one.
Reformed and Lutheran churches abolished saints' days, closed shrines and stripped altars of images within a generation, and the divide has held: most Protestant traditions still regard prayer to the saints as a practice with no biblical basis, whatever pastoral value Catholics and Orthodox claim for it. Marian apparitions supply the clearest instance of how the devotion actually spreads.
At Guadalupe in 1531, an apparition reported by an indigenous convert, Juan Diego, produced an image on his cloak that became the object of the most visited Marian shrine in the world and, within a few generations, a central symbol of Mexican and wider Latin American Catholic identity, cited by clergy at the time as instrumental in the mass conversion of the indigenous population. The Catholic church treats such apparitions cautiously and formally, requiring a bishop's investigation and a finding of worthy of belief before public devotion is approved, which keeps the vast majority of reported apparitions worldwide without official recognition even where local devotion is intense. Guadalupe's case shows both halves of the practice at once: an intercessory devotion that Rome polices carefully, and a popular movement that routinely outruns any formal approval it receives.