Relying on Tafsir al-Mizan, this article presents definitions for ethics and purification of soul from the viewpoint of Allameh Tabatabaee. Relying on the principle of monotheism, it also proves that a monotheistic ethical system is the most progressive ethical system which considers all the personal and social affairs of man along each other in order to fulfill a common objective, i.e. Devine unity, following the strategy of eradicating vices instead of repelling them.