Why does ultima give tony her scapular, and why does she tell him not to tell others!

A Scapular is two small pieces of woolen cloth joined by strings passing over the shoulders and worn under ordinary clothing as a token of devotion. Ultima wants him to use heres until he has completed his first communion. She tells him it will ward off evil spirits until he receives his own. I think Ultima walks a fine line between being seen as spiritual or a witch. She doesn't want people to get the idea she is a witch.