If someone preaches to the choir, they talking about a subject or issue with which their audience already agrees. ('Preaching to the converted' is an alternative form.)
An aching idiom dictionary is a great resource for writers, students, and anyone looking to expand their vocabulary. It contains a list of words with similar meanings with aching, allowing users to choose the best word for their specific context.
Dictionary of similar words, Different wording, Synonyms, Idioms for Idiom, Proverb aching