Tanya Chapter 6 part 1. The fight between good and evil has to be fair

Hashem created "one thing opposite the other." This means that all ten powers of the Divine soul have a corresponding counterpart in the animal soul, along with the three garments, or modes of expression. The emotional qualities of the animal soul are aligned with its intellectual nature.How do we identify a thought, word, or action as an expression of the animal soul? And how do we recognize what belongs to "sitra achra -- the other side"? Anything not directed towards Hashem is automatically aligned with "the other side."And how do we define holiness? Anything surrendered to the Divine is called holy—like the angels, who are in a constant, actualized state of surrender, or the Jewish person who would give up their life in martyrdom for the sake of Hashem.