preach to the converted
Try to convince someone who is already convinced, as in Why tell me smoking is bad when I gave it up years ago? You're preaching to the converted. [Mid-1800s]
Words nearby preach to the converted
pre-raphaelite,
pre-roman,
pre-socratic,
pre-u,
preach,
preach to the converted,
preacher,
preacher curl,
preachify,
preaching,
preachment