We wear scapulars because they were given to us by the Blessed Mother along with a promise.
These scapulars (a word meaning “shoulders” in Latin) are a sign of devotion to Mary and faithfulness to Christ. The original scapular was large piece of brown cloth worn over the shoulders of monks.
According to Catholic tradition, Our Lady gave the scapular to St. Simon Stock, the Father General of the Carmelite order, in the thirteenth century. Mary appeared to St. Simon in a vision, held out a scapular and said to him, ' . . . he who dies in this will not suffer eternal fire.'
Does this mean if you wear the scapular you get into heaven no matter what your actions? Of course not!
The scapular is not a “get out of hell free” card or a magical charm. It is an exterior sign of an interior fidelity to Christ and trust in his Mother's love and intercession for her children.
In some ways it’s like a wedding ring. A husband and wife wear wedding rings to show their interior fidelity to each other. Similarly, when Catholics wear a scapular they are showing outwardly their love of Mary and commitment to Christ.
However, the scapular is more than just a sign. It is a Sacramental! Sacramentals are sacred signs that prepare us to receive grace and help us to be in a disposition to cooperate with that grace (CCC 1670).
Wearing a scapular can actually help prepare you to receive grace and therefore help you grow in holiness! Mary Our Mother gives us, her children, the gift of the scapular as both a sign and a tool for us to help us grow closer to her Son, which is always her desire.