Complex sentence: The cardinal virtues are the properties of virtue which immediately flow from its very essence and have nothing to do with externals: diligence, obedience, justice, humility (III, 17).
Split into simpler sentences: The cardinal virtues are the properties of virtue which immediately flow from its very essence and have nothing to do with anything external. These properties are diligence, obedience, justice, humility (III, 17).