Marriage obbligato

Obbligato is a musical term that means an indispensable part of a piece. The piccolo solo in Sousa's Stars and Stripes Forever is labeled obbligato.
It's never to be cut.
Obbligato comes from an Italian word that means to obligate. Marriage is an obligation. That means it is a requirement that must be fulfilled. The Italian root word obbligare means to compel or bind (duty bound).
An obligation is an act of binding oneself.