Leavening is an agent that causes change, typically through fermentation. The ingredients break down in a biochemical reaction that produces carbon dioxide, which causes expansion. The original ingredients are changed from what they were through a reaction that will keep going as long as there are ingredients that can fuel it. So, leaven spreads.
In its broadest sense, leaven is a symbol of corruption. It includes sin, but it is not limited to sin because it also includes the ideas, philosophies, and approaches that lead to sin. This connects with what we saw in Galatians. The Galatians (and Colossians) were being influenced by philosophies and doctrines that would lead them into bondage. Leavening was corrupting them, and a new slavery would be the result if they didn’t return to Christ.
Here, Paul says a little leaven leavens the whole lump. He uses the same phrase in Galatians 5:9. In the verse that comes right before that, Paul calls the heresy that was corrupting the Galatians a “persuasion.” Paul says, “This persuasion does not come from Him who calls you.” So, leavening can be an idea that persuades us to deviate from the truth, even as our minds may feel like they are expanding.
This fits with the various warnings Jesus gave about leavening. He warned about the leaven of the Pharisees, the leaven of the Sadducees, and the leaven of Herod. In each case, leavening is a symbol for corrupted ideas that lead to a wrong application.
In Matthew 16:12, we find that part of the leaven of the Pharisees was their doctrines, which elevated tradition above the word of God. Another part of their leaven was hypocrisy. They focused more on appearing righteous than being righteous. Jesus said of the Pharisees, “they say, and do not do” (Matthew 23:3). They exempted themselves from the standard they held others to. While they looked good, their self-centeredness and self-generated standard of righteousness made life very difficult for those caught in their orbit.
The leaven of the Sadducees was their corrupted teachings and attitudes, like skepticism, that undermined the essential doctrines of faith. As two examples, the Sadducees denied the resurrection and they denied the existence of angels. That is a significant corruption.
The leaven of Herod is interesting because of the politics of our day. It is not clearly defined, so we have to read between the lines. But from what we know of Herod, his leaven seems to be a worldly pragmatism, and an overall disregard for spiritual truth in favor of power. His corruption seems to include the use of religion for political ends. Herod wouldn’t stop his adoring crowd from likening him to God, and God struck him dead.
Here in I Corinthians 5, Paul uses malice and wickedness as additional types of leaven. Malice is an internal disposition, while wickedness is an outward manifestation. We can tell from the rest of the epistle that these corruptions were affecting the congregation, which is why Paul brought attention to them.
