"Whosoever dies clothed in this Scapular shall not suffer eternal fire."
According to tradition, this was the promise made by Our Lady on July 16, 1251 to St. Simon Stock, an early prior general of the Carmelite order.
The history of the scapular predates St. Simon, originating in the mantle of Elijah. To bring the people back from their worship of the false god Baal the prophet prayed for a drought, which lasted for three and a half years. At that time Elijah climbed Mt. Carmel to petition for the rain to return. After praying six times to no avail, a cloud in the shape of a foot was seen coming over the sea, growing until it had covered the sky and eventually breaking to provide much-needed rain.
Pious tradition holds the cloud represented Our Lady, as its shape corresponded with the prophecy of Genesis in which the foot of the Woman would crush the serpent's head; additionally the cloud, which formed out of the salty sea, poured out fresh water, which is said to mirror the Immaculate Conception. A third belief sees an allusion to Mary as the Mediatrix of graces, for out of a single cloud flowed an immense quantity of rain, or grace, which quenched the parched desert.
Following the event, Elijah formed a community of hermits on Mt. Carmel, and it was out of this community the Carmelite Order was born in the late 11th century.
The apparition to St. Simon occurred as the newly formed order was in the throes of persecution as well as political strife within the congregation itself. It is believed that during an intense session of prayer, Our Lady, accompanied by a host of angels, appeared to St. Simon and presented him with the scapular, saying, "Take, beloved son, this scapular of thy order as a badge of my confraternity and for thee and all Carmelites a special sign of grace; whoever dies in this garment will not suffer everlasting fire. It is the sign of salvation, a safeguard in dangers, a pledge of peace and of the covenant."
Following the promulgation of the brown scapular among the Carmelites, the troubles that had afflicted them all but vanished: the order became recognized by its peers, the internal strife ceased and the community's Marian devotion was solidified.
Pope St. John Paul II was also known for his devotion to the sacramental, famously instructing surgeons to leave his scapular on him during the operation after the 1981 assassination attempt. Of this sacramental, the pope said:
The sign of the Scapular points to an effective synthesis of Marian spirituality, which nourishes the devotion of believers and makes them sensitive to the Virgin Mother's loving presence in their lives. ... [D]evotion to her cannot be limited to prayers and tributes in her honor on certain occasions, but must become a "habit," that is, a permanent orientation of one's own Christian conduct.