I often reflect on the role it filled for mental health before the advent of science, psychology, and neuropsychiatry.

I was raised in a very opressive sect of protestantism, where I was instructed to pray and meditate. I find it analogus to visualisation and self reflection. I learned silence and meditation, I was put in situations where sitting silent by the hour listening to empty droning speech was my only recourse. My first awareness of the concept of mental illness was from bible stories of those people being healed implying their condition was not inherent to them, they were innocent.

The act of singing together about our beliefs and feelings has always seemed like a powerful thing that has vanished from our society, except at baseball games.

Right, so oppression.

It's also commonly used to create a strong sense of "us"/"them", inferiority to the unquestionable elite, superiority and self righteousness over non-believers, and a great way to force your underlings to do your bidding disguised as words from "God", whoever that might be.

Also an explanation for things we couldn't explain. Humans hate uncertainty and randomness. A random flood is scary because it could repeat without warning, but if it happened because you pissed off the gods then you can just avoid doing that and you're safe.