The American Heritage Dictionary defines leaven as “an agent, such as yeast, that causes batter or dough to rise, especially by fermentation.” The term “leaven” is mentioned 24 times in the Bible. Sometimes it is used in a literal sense (Lev. 23:17); such as we read in the above definition. However, the term is often used in a figurative sense to denote a pervasive influence that is either good or bad.
Jesus used the term in a negative sense when He warned His disciples about the doctrine of the Pharisees, Sadducees (Matt. 16:6, 11-12), and Herod (Mk. 8:15). This warning still resonates today, for the pervasive influence of false doctrine will result in eternal condemnation for those who preach it and for those who embrace it (Gal. 1:8-9).
The bad leaven of corruption is found wherever sin is tolerated. This is why Christians must abstain from the evil influences of the world lest they too be condemned with the world (cf. Matt. 5:27-30; Rom. 8: 5-8). “Be not deceived: Evil companionships corrupt good morals” (1 Cor. 15:33). “Do you not know that a little leaven leavens the whole lump? Therefore purge out the old leaven” (5:6-7)
On the other hand, Jesus also used the term “leaven” in a good sense. He said, “The kingdom of heaven is like leaven, which a woman took and hid in three measures of meal till it was all leavened” (Matt. 13:33).
Think of it, leaven does its work from within; and that’s how the influence of the gospel of Christ works (it works within a person’s heart – Jas. 1:21; Lk. 8:15). Think of it, leaven changes the ingredients; and that’s what the word of God does. When one accepts the gospel they become a new man (Rom. 6:4), having new thoughts (Col. 3:1-4), and doing new deeds (vv. 5-17). Think of it, leaven is aggressive (it does not stop until it has affected the whole); and that’s how New Testament Christianity works. The kingdom of God is spread by the pervasive influence of those who are Christ’s, who bring others to Him (cf. Jn. 1: 40-45), who introduce His saving message to them (Acts 8:4, 12).
Whether good or bad, “a little leaven leavens the whole lump.” Friend, what are the influences in your life?