“Celebrate the Feast of Unleavened Bread” (Exodus 12:17 NIV). Leavening is the process of aerating bread dough. Typically the leavening agent is yeast, a microorganism from the fungi kingdom which is used to turn starches and sugars into carbon dioxide. Most strains of yeast reproduce exponentially when introduced to the right environment, such as flour and water. Leavening is mentioned in many places in the Bible. It is used in the Old Testament as a commandment as well as an illustration tool in the New Testament. Close examination will show that it has the same figurative meaning in both scenarios.