preach

preach /ˈpriːtʃ/ verb
preaches; preached; preaching
preach
/ˈpriːtʃ/
verb
preaches; preached; preaching
Britannica Dictionary definition of PREACH
1 
: to make a speech about religion in a church or other public place : to deliver a sermon
[no object]
[+ object]
2 
: to write or speak about (something) in an approving way : to say that (something) is good or necessary
[+ object]
[no object]
3 
[no object] : to write or speak in an annoying way about the right way to behave

preach to the choir

(chiefly US) or preach to the converted
: to speak for or against something to people who already agree with your opinions