There’s a point in “The Oratorio” when the attention turns to the organ at St. Patrick’s Old Cathedral in New York City. The giant instrument is both a vestige and a living example of the long history of the church, located on Mulberry Street near Chinatown and Little Italy in Manhattan. With key parts made from wood and leather, it’s something for which continued existence isn’t a guarantee.

It has to be nurtured if it’s going to continue on in its current form. “The Oratorio” doesn’t lean into the metaphor, but for a documentary about opera, it’s hard not to see it as a perfect representation of another institution that has survived with the help of people keeping it alive.