Physically, leaven is a lump of old dough in a high state of fermentation, or a substance that causes dough to rise (yeast). A natural reason for leaven's negative symbolism is the idea that fermentation implies a process of corruption. In the Old Testament, it is generally symbolic of sin and evil. In every instance that leaven appears in the Bible, it represents evil; the only exception, some say, is Jesus' use of leaven in this parable. Knowing its Old Testament significance, however, He would have used the symbol in the same way.
While some commentaries interpret this parable as depicting the spreading influence of the gospel, such explanations go against Jesus' use of this symbol. He uses it to refer to the evil doctrine of the Pharisees, the Sadducees, and Herod (Matthew 16:6-12; Mark 8:15), and this could easily apply to later corruptions of doctrine by those who place more importance on the traditions of men than on the Word of God.
Paul uses leavening as a type of sin in its development (I Corinthians 5:6-8). His reference to Christ's sinless sacrifice, and his statement that believers, as such, are unleavened shows the typical significance of leaven. In Galatians 5:7-9, its diffusive quality describes the harmful effects of false doctrine. He calls leaven a persuasion, something that exerts a powerful and moving influence, that hinders people from obeying the truth. Such a thing, he declares, is not from Him who calls us.
In the parable, the leaven alone is not what relates to the Kingdom, but the entire concept in the parable, the progress of the church in history. The leaven is hidden in the meal, representing the way Satan subtly strikes against the truth. Leaven is symbolic of things that disintegrate, break up, and corrupt. The leaven of the Pharisees was hypocritical formality. That of the Sadducees was skepticism. Herod's was of shameful self-indulgence in worldly desires. The leaven of those who have distorted doctrine down through the ages has been greed, pride, control, and worldly desires.
Whenever we find the symbol of a woman in the Bible, she represents a system of beliefs and practices that influence other people. Nations or political groups and religions or churches have specific unique beliefs. All human-based belief systems go contrary to God because "the carnal mind is enmity against God" (Romans 8:7). What the woman does and how she acts determines what belief system she is representing.
The woman in the parable takes leaven and hides it in the meal (Matthew 13:33). Hid is translated from the Greek word enkrupto, from which comes the English word "encrypt." The root word, krupto, means "to conceal" or "to keep secret." Hence, this woman is surreptitiously placing the leaven of false doctrine in the church. She is an opponent of Christ and infuses His church with corrupting ideas. Elsewhere she is called "Wickedness" (Zechariah 5:7-8), "Jezebel" (Revelation 2:20), and the "great harlot" (Revelation 17:1).
Three measures of meal would be a huge amount even for a large family - perhaps as much as is needed to make about a dozen loaves of bread. More importantly, most of the Jews listening to Jesus would have recognized the three measures of meal (an ephah) as the meal or grain offering (Leviticus 2). This offering was never allowed to contain leaven (Leviticus 2:5). The meal offering represents the offerer's service and loyalty to his fellow man and is typified in how Jesus Christ offered Himself in service to mankind (Matthew 20:25-28). It portrays the second great commandment of Matthew 22:36-39: love of our fellow human beings. Thus, the three measures of meal represent love, service, and loyalty to others, specifically our brethren in the church.
Jesus warns in this parable that false doctrines would be infused by stealth into the church, and these evil beliefs would corrupt, erode, and destroy relationships. If the false doctrines are allowed to grow, affection and loving concern in service to one another are thwarted. The phrase "till all was leavened" is a sobering indication that the church would be plagued by insensitive, uncaring, self-absorbed, self-centered attitudes that would spread through the church just as leaven spreads through bread dough. The apostle Paul tells us "through love serve one another" (Galatians 5:13), an antidote to the woman's devious subterfuge.