Class 16, Perek 1, Class 6 Tanya (text based)

סטרא אחרא vs. צד הקדושה. On earth there are three levels and ideas: 1) חוב and 2) איסור, and 3) רשות. On the תורה שבשמים level, if it isn’t holy it is automatically anti-holy. This is why all that is not holy is סטרא אחרא וקליפה. In other words it is טומאה.