be preaching to the converted

be preaching to the converted

If someone is preaching to the converted, they are presenting an opinion or argument to people who already agree with them. You're wasting your time preaching to the converted. In any case the film was, by and large, preaching to the converted. Note: The converted are people who have converted, or changed their religious beliefs. Preaching is the activity of telling people about a religion.
See also: convert, preach