In Luke 13:20-21, Jesus told this parable: “To what shall I liken the kingdom of God? It is like leaven, which a woman took and hid in three measures of meal till it was all leavened.”

Leaven, for the non-cooks among us, is the substance used to make bread dough rise. Commonly we use dry yeast today. In Biblical times, people used an actively fermenting dough, much like our sourdough starter. The Lord uses the figure of leaven to make a positive point: that the kingdom of God can have a pervasive influence if that influence is provided opportunity. The leavening agent had no effect on the meal used to make the dough until the leaven was “hidden” within the meal. Think of trying to make bread dough by dropping an unopened packet of yeast into the mixing bowl!

As citizens of the heavenly kingdom, we can have a powerful effect on those around us. But we can’t have that effect in isolation. We have to be “hidden” among the people of the world. We have to associate with and exercise our influence on others.

Many times we might think we would be better off if we gathered together with other Christians and established our own community somewhere far from the evils of society. And perhaps in some selfish ways, that might be so. But we have a responsibility to Christ to carry the gospel forward, to “make disciples of all the nations” (Matthew 28:19). We can’t accomplish that work if the only people we ever see are those who are already disciples. It’s akin to trying to catch fish at the fish market: those fish have already been caught! To catch new fish, one must take line and tackle and rod and bait and go where the fish are.

But how then do we observe the instruction of God that says, “Come out from among them and be separate, says the Lord; do not touch what is unclean and I will receive you” (2 Corinthians 6:17)? If we’re to be separate, how can we associate with the world?

What we have to understand about leaven—or to apply this metaphor, the power of influence—is that it works in two directions. Even as Christians have a duty to leaven the world by means of our influence, we also have a duty not to become leavened—unduly influenced—by the world. It’s the same thing Jesus said concerning salt: “You are the salt of the earth; but if the salt loses its flavor, how shall it be seasoned? It is then good for nothing but to be thrown out and trampled underfoot by men” (Matthew 5:13). In order to be “salt of the earth,” we must maintain our unique character. If we take on the character of our environment, we cease to be “salty.”

Paul reminds us that it doesn’t require a great deal of influence to have a marked effect. “Do you not know that a little leaven leavens the whole lump?” (1 Corinthians 5:6). We might think that a small amount of worldly influence won’t do us any harm. Think again! It takes very little to sway our minds in one direction or another. We must be very careful about the leaven that surrounds us—recognize it for what it is, and resist its temptations.

The reverse, of course, can also be true. We can exert a compelling influence on other people in seemingly small ways. Consider some of the tiny acts of righteousness that are preserved for us in the Bible: the widow’s two coins (Luke 21:1-4); the charity of Tabitha (Acts 9:39); the young lad who gave his lunch to feed a multitude (John 6:9); the generosity of Barnabas (Acts 4:36-37); the anointing of Jesus by Mary of Bethany (Mark 14:3-9). Don’t these good deeds still “leaven” us today? If that is so, who knows what ripple effect our godly living and faithful service might achieve?

We must understand that leavening is an either/or proposition. Either we will leaven others, or we will be leavened. Either we will exert a positive influence on the world, or the world will have a negative influence on us. Both cannot be true simultaneously—we can’t be a good influence while we are being wrongly influenced. If we want to be leaven, we can’t allow ourselves to be leavened. By the same token, if we are absorbing the leaven of the unrighteous world, we aren’t of much use as a righteous leavening agent.

Look at your life. Are you leavening the world, or are you just getting leavened? You control the stream of influence, whether it flows outwardly from you or inwardly to you. Which will it be—you leavening the dough, or the dough leavening you?