Question
What is the spirtual significance of leaven?
Answer
Leaven is forbidden on Passover to remind us that our ancestors left Egypt in a hurry and didn't have time for their dough to rise (Ex.12:34,39). In addition, leaven has become symbolic of the evil inclination, which the Talmud (Berachos 17a) refers to as "the leaven in the dough". But actual leaven is forbidden only on Passover; it may symbolize the evil inclination, but it isn't itself regarded as evil.