Garfield by Jim Davis, 06 July 2010 at Go Comics
‘To preach to the choir’ is a very common American expression that means to try to persuade people to accept opinions or beliefs that they already have. We often use the expression to show our agreement or support such as in:
“I agree with you entirely; you’re preaching to the choir."
The allusion is made of a preacher in a church and the choir behind him. The choir of course is the group of singers who sing the hymns and are already believers in the church. The preacher’s job is to preach and to convert the non-believers.
Another variation of the same expression is “to preach to the converted.” Such as in the example:
“You don’t need to tell me how important it is to finish this project on time; you’re preaching to the converted.”
Note: burp = un rot, roter