Chametz is the yetzer hara [the evil inclination] as the Rambam explained that chametz comes from the expression for stealing...since whoever goes according to the advice of the yetzer hara steals from their [soul] root.
Rabbi Kerry Olitzky "Spiritual Hametz"
This leaven, this hametz, also symbolizes a puffiness of self, an inflated personality, an egocentricity that threatens to eclipse the essential personality of the individual. Ironically, it is what prevents the individual from rising spiritually and moving closer to holiness.
You must never allow your Divinely-given intellect to be infected in the least by the chametz — yeast — of these fallacious beliefs...They distort and sully the mind, making it impossible to concentrate while praying or to experience real joy...The main thing is to guard the mind against “yeast” by avoiding all bad thoughts.
This is the difference between chametz and matzah, which is the difference between the chet and the heh. Chametz is [spelled] with a CheT. This is the aspect of peace without a mouth, the aspect of the “living,” the aspect of “the ChaiyaT (beast) of the field will make peace with you” (Job 5:23)—i.e., the aspect of peace that has no mouth, that lacks the power of speech, like the beasts of the field.
There is chametz — leaven — in a person’s heart which induces him to have doubts about the leading Sages of his time, deciding that “This one is all right, that one is no good,” etc.
