Not a hate soapbox: Watching a movie called Tommy Boy...?

The scene I am at is a wedding scene. A non-secular person is officiating the wedding but at the conclusion of the vows the priest says "By the power vested in me by the state of ______ I now pronounce you man and wife"...that's where I got a little confused. Throughout history a select few groups of individuals had the traditional right to conduct a legitimate marriage. Why would a RC or Anglican minister require the permission of a secular institution to perform a religious tradition?