The Bible tells us that the Israelites were to eat only unleavened bread every year during Passover as a commemoration of the Exodus from Egyptian bondage. Since the children of Israel left Egypt hastily, they did not have time for the bread to rise, so it was made on that very first Passover without leaven, also known as yeast. In describing this bread and why it was eaten, the Bible informs us of the following: “Do not eat it with bread made with yeast, but for seven days eat unleavened bread, the bread of affliction, because you left Egypt in haste—so that all the days of your life you may remember the time of your departure from Egypt” (Deuteronomy 16:3). Further commands regarding the eating of unleavened bread are found in Exodus 12:8; 29:2; and Numbers 9:11. To this day, in Jewish homes, the Passover celebration includes unleavened bread.
According to the Hebrew lexicon, the term “unleavened bread” is derived from the word matzoh, which means “bread or cake without leaven.” The lexicon also states that matzoh is in turn derived from a word which means “to drain out or suck.” In referring to this second Hebrew word, the lexicon states, “In the sense of greedily devouring for sweetness.” So it is quite possible that unleavened bread, while it may have been heavy and flat, may also have been sweet to the taste.
In the Bible, leaven is almost always symbolic of sin. Like leaven which permeates the whole lump of dough, sin will spread in a person, a church or a nation, eventually overwhelming and bringing its participants into its bondage and eventually to death. Romans 6:23 tell us that “the wages of sin is death,” which is God’s judgment for sin, and this is the reason that Christ died—to provide a way out of this judgment for sin if man will repent of his sins, accept Christ as his Passover sacrifice, and have his heart changed so that he can conform his life to what God commands.
Whenever a little bit of sin in a person or a church is permitted, overlooked, and compromised, it works much like leaven in bread. It will eventually leaven the whole lump, affecting the whole church or the whole world (Galatians 5:9). This permitted sin will lead to other sins and will eventually draw a person or church completely outside of the will and favor of our Father, and our Savior, Jesus Christ.
 Got Questions Ministries. (2010). Got Questions? Bible Questions Answered. Bellingham, WA: Logos Bible Software.