The next parable in Matthew is found in a single verse. In 13:33, Jesus compares the kingdom of heaven to leaven. It involves a woman, hiding of leaven, three measures of meal, time, and work. At face value, one might suggest that the woman is the Church who permeates the world with the gospel, until the whole world is saved. Amillennialists, those who do not believe in a literal thousand year reign of Christ on earth, believe that the Church will eventually win the world for Christ. But notice that Jesus has gone from the "good soil," and the "wheat," to a useless tree, and now leavened bread. There is a progression from taking the Gospel away, to infiltrating, to providing lodging to the enemy, and here, effecting the whole loaf. If we view the loaf as the world, and leaven as good, then things would be improving, but such is not the case.
Webster's Dictionary says that leavening is the process whereby yeast, a tiny single-celled fungi which give off carbon dioxide or gas. When used to leaven bread, the yeast produces gas bubbles to form. When this occurs, the dough is said to be "rising." Normally, that would be a good thing, right? However, when used in the Bible, leaven represents sin. In 1 Corinthians 5:1-9, sin is described as leaven which, if left unchecked, will effect the entire Church. Paul tells the Corinthian church to purge itself of leaven (sin). He adds that a "little leaven (in this case, legalism) leaveneth the whole lump in Galatians 5:9.
Jesus warns His disciples to beware of the leaven (false doctrine) of the pharisees and the Sadducess in all three synoptic gospels: Matthew 16:6, 11-12; Mark 8:15; and in Luke 12:1. John does not mention leaven. All of Israel understood what leaven was. When Passover and the Feast of Unleavened Bread were celebrated in the first month of Israel's calendar, Israel was repeatedly warned to purge their entire dwelling place of all leaven (numerous references). I am not certain if they understood why, but Christians clearly understand today. The Passover was the holiday on which the lamb was sacrificed, and it commemorated Israel's release from Egyptian bondage. To the Christian, Passover was a picture of the ultimate sacrifice of the Lamb of God. John the Baptist called Jesus "the Lamb of God Who taketh away the sin of the world" in John 1:29, and Paul called Jesus "our Passover" in 1 Corinthians 5:7. In the Lord's Supper, the bread (unleavened) represents the body of Jesus, and the "wine" represents His blood. Since wine also requires fermentation, the drink must have been grape juice, or having unleavened bread would be contradictory.
As can be seen, leaven is representative of sin. In the parable, then, the woman must represent someone who hides sin in the whole loaf. The loaf, like the tree, represents the Church. It is easy to discern who the woman represents: Satan. He, if nothing else, is consistent. Our enemy is always vigilant. seeking whom he may devour (1 Peter 5:8). Wear your armor, my brothers and sisters (Ephesians 6:10-12).