Jamieson, Fausset & Brown

not . . . old leaven--of our unconverted state as Jews or heathen. malice--the opposite of "sincerity," which allows no leaven of evil to be mixed up with good (Mat 16:6). wickedness--the opposite of "truth," which allows not evil to be mistaken for good. The Greek for "malice" means the evil habit of mind; "wickedness," the outcoming of the same in word and deed. The Greek for "sincerity" expresses literally, a thing which, when examined by the sun's light, is found pure and unadulterated.