[passionfruit]

“The relic of St. Therese of Lisieux, patron saint of missions, is a small piece of her body — about the size of a quarter — which could have easily fit in the pocket of the thief.”

This poor nun died at a young age and they cut out a part of her body to keep? She wasn't even canonized for nearly another 30 years!

I don't understand Catholicism at all!

[annalex]

they cut out a part of her body to keep?

No, of course not. Her relics were probably retrieved following canonization so that the faithful have a chance to venerate them.