Complex sentence: Usury (lending money with interest) was illegal for Christians to practice, according to Church law it was seen as a vice in which people profited from others' misfortune (like gambling), and was punishable by excommunication, a severe punishment.
Split into simpler sentences: Usury (lending money with interest) was illegal for Christians to practice. According to Church law it was seen as a vice in which people profited from others' misfortune (like gambling), and was punishable by excommunication, a severe punishment.