تعریف و معنای "[sing] from the same hymn book"

What is the origin of the idiom "sing from the same hymn book" and when to use it?

The phrase "sing from the same hymn book" is an idiom that is believed to have originated in the 17th century, when hymns were a common form of religious music. When people sang from the same hymn book, it meant that they were all singing the same words, which was seen as a symbol of unity and agreement. This expression is used to describe a group of people who are in agreement, have the same opinion, or act in a coordinated fashion.