I still occasionally hear "Morning Has Broken" by Cat Stevens.
I went to a YMCA camp in the 70s, they pushed religion hard and frequently played "Morning Has Broken". That's when I first realized it was a religious song.
Somewhat ironic, considering that he later became a muslim (now known as Yusef Islam or something like that). I only knew that it was considered a "religious" song from seeing it in church hymnals! I don't recall ever actually hearing it sung in church, although I seem to remember hearing it sung in a church service that was broadcast over the radio.