I ran across this question, and I'm wondering if someone can give me more information on what a Scapular is, and what, exactly, the significance and/or theology goes along with it?
The Scapular was given to St. Simon Stock, a Carmelite monk.
It's essentially two small pieces of wool attached by two 18 inch cords with the words (in the vernacular) "Whosoever dies wearing this scapular will not suffer eternal fire".
For this reason, I wear a scapular all the time, except when I take a shower and then I am very careful not to drop the soap.
If you want to associate a theology with the scapular, then I guess it would have to be Carmelite spirituality which is austere, loving and personal. St. Theresa of Avila and St. John of the Cross would be good starting points to know about Carmelite Spirituality. St. Therese of Lisieux too, but she came along long after the first two and her words are, well they're just amazing.
In any event, I think the priest who answered my question you linked to gave a good explanation of what one needs to do in conjunction with the scapular. It's a sacramental and a devotion. It should be blessed by a priest and the prayers should be recited every night. But it's not magic and by itself will not pull your soul out of hell. I think it was made as a small mortification, which fits in excellently with St. Therese's little way. It's two itchy spots on your chest and back that. If you've got a decision that makes you sweat a little, will pull you back in to reality. It works a bit better than a WWJD bracelet, but in this sense is the same thing.