What does Paul mean by 'a little leaven leaveneth the whole lump'?

In Galatians 5:9, Paul warns that just as a small amount of leaven can cause dough to rise, so too can a small amount of false teaching lead to spiritual corruption within the church. The Judaizers were introducing teachings that required works of the law for righteousness, which undermined the gospel's message of grace. This principle serves as a reminder to be vigilant against compromise in our beliefs, as even minor deviations from the truth can have significant consequences for the community of faith. It underscores the importance of maintaining sound doctrine and safeguarding the purity of the gospel.