preach to the choir

In agreement or sharing the same understanding.

an unpleasant piece of information; (informal) a person or thing likely to cause trouble

used to say that things have gone well up to now

To do or say something that eases tension and gets people talking comfortably in an unfamiliar social situation.

to return to a topic or person later, after other things have happened

to give false warnings so often that a real warning may later be ignored