Matthew 13:33 “He told them still another parable:” The kingdom of heaven is like yeast that a woman took and mixed into a large amount of flour until it worked all through the dough.”
Yeast in the Old Testament is symbolic of evil doctrines, malice and wickedness. It is a type of sin.
Yeast looks like a minor ingredient but a little spoon of it permeates to increase the size of a mound of dough several times.
In this parable yeast sounds like a positive symbol of growth. The Kingdom of God began small and looked insignificant, but it has grown to have the greatest impact on earth that the world has ever known.