To him that knoweth (eidoti). Dative case of second perfect participle eidw (from oida), and with the infinitive to know how, "to one knowing how." To do good (kalon poiein). "To do a good deed." And doeth it not (kai mh poiounti). Dative again of the present active participle of poiew, "and to one not doing it." Cf. "not a doer" ( 1 Thessalonians 1:23 ) and Matthew 7:26 . Sin (amartia). Unused knowledge of one's duty is sin, the sin of omission. Cf. Matthew 23:23 .