It was given to Simon Stock by Our Lady of Mount Carmel, who promised him that "whoever dies clothed in this scapular shall not suffer the eternal flames."
Later, she appeared to Pope John XXII as the Mediatrix of all graces, promising him that "whoever shall wear my Scapular faithfully, pray the Divine Office [various indults have applied in the past and apply today], and exercise chastity in their state of life shall not suffer Hell, and if they should go to Purgatory, I shall bring them to Heaven on the First Saturday after their death" (Sabbatine Privilege).
The Blue Scapular (also known as the Scapular of the Immaculate Conception) is due to Venerable Ursula Benincasa, founder of the Order of Theatine Nuns, when a group of wealthy young women who had given up their wealth in order to live for Jesus Christ had wanted to honor the Immaculate Conception of the Blessed Virgin Mary.
The Lord promised that whoever wore his Scapular would be granted a great increase of faith, hope, and charity every Friday (the office day of the Passion).
The apparition was repeated several times, and in the following year Pope Pius IX sanctified the sacramental on June 25, 1857.