The “belt of truth” refers to a leather belt with an apron that hung at the front of a Roman soldier’s groin and lower abdomen. Small brass plates were attached to the apron in or order to provide more protection.
In preparation for battle, this belt would be put on first. The belt prepares a soldier for action. The admonition to have “your loins girt about with truth” is a call to Christians be ready to defend themselves and not be caught unawares by the powers of darkness.
Stand therefore, having your loins girt about with truth, and having on the breastplate of righteousness; Eph 6:14