There are two types of leaven: Physical and Spiritual.
Physical leaven is an agent like yeast that is introduced into a lump of dough. The yeast produces bubbles of gas in the process called fermentation. These bubbles spread throughout the entire lump of dough causing the dough to rise. This is how a typical loaf of bread is made.
Spiritual leaven is anything we allow into our lives contrary to the word of God. Allowing spiritual leaven into our lives can lead to SINFUL BEHAVIOR.
So, when the Apostle Paul says in Gal 5:9, "A little leaven leavens the whole lump,' what is he saying to the Galatians and to us?
He's saying that a little bit of 'untruth,' a little bit of 'false teaching,' a little bit of 'impure thoughts' is leaven that can affect and transform the whole person.
Leaven is allowed in through the mind (thoughts), then seeps into the heart, creating a desire. That desire, if strong enough, can