4:2

conscience is seared as with a branding iron: In Paul’s day, as a sign of a person’s ownership, a branding iron might be used to burn a mark into the skin of livestock. As a result, the burned flesh of the animal would form scar tissue and become insensitive. Paul here uses a form of the Greek word kau·ste·ri·aʹzo·mai (lit., “to be branded with a red-hot iron”), perhaps to show that when a person persistently does what is wrong, his conscience becomes insensitive. He no longer feels reluctant to do what is bad; nor does he feel guilty after he does it. (Compare study note on Eph 4:19.) Some scholars suggest a different meaning, namely, that the consciences of persistent wrongdoers are figuratively branded, or marked, to indicate that the wrongdoers are owned by Satan and the demons.