Another long simile Jesus told is about how the kingdom is like a woman baking bread. Part of the bread making process is mixing yeast into the dough. Yeast is added, and the baker kneads and rolls the dough until the yeast is thoroughly dispersed throughout the dough. A chemical reaction releases carbon dioxide into the dough and the changes the whole texture of the dough. The changing the nature of the bread is done from the inside. It happens as the yeast carries out its natural function.
The yeast is like the kingdom. As it lives out its normal functions, it affects the texture, taste and nature of the society it is immersed in.