The introduction of leaven

[Suannehill]

By tradition and teaching...leaven is negative in both Christian and Jewish faiths.
We can't avoid leaven on this earth.
As a baker of yeast breads since a child I can tell you that yeast is everywhere. In fact, that's what sourdough bread is...wild yeast...just expose it to the air.
Vinegar is made with wild yeast from the air and don't forget our bodies, some of the most resistant infections are yeast.
So, it's easy to see positive and and negative aspects of yeast.
However, spiritually...yeast is negative.