Bible Dictionary
SEAR
To have the conscience seared means to have it made insensitive, like flesh cauterized by a hot iron. The passage may also suggest being branded as a mark of hypocrisy and guilt.
Biblical Usage
First Timothy 4:2 speaks of people whose consciences are seared or branded. The image describes an inward moral insensibility, compared with the loss of feeling in the surface of a deep burn after healing.