preach to the choir
US /priːtʃ tu ðə kwaɪər/
UK /priːtʃ tu ðə kwaɪər/

1.
對牛彈琴, 向已相信的人說教
to try to persuade people to believe things that they already believe
:
•
When I talk about the importance of environmental protection to this group, I feel like I'm preaching to the choir.
當我向這個團體談論環境保護的重要性時,我覺得我是在對牛彈琴。
•
You don't need to convince me; you're preaching to the choir.
你不需要說服我;你是在對牛彈琴。