Leaven (Yeast)

Leaven was a piece of fermented old dough worked into a fresh batch; unseen, it permeated the whole lump and made it rise. Because fermentation looked like a kind of corruption, and because Israel left Egypt too fast for bread to rise, leaven was purged from every home during Passover and Unleavened Bread.

From this came its main symbolic use: a small hidden influence that spreads through everything. “A little leaven leaveneth the whole lump,” Paul warns about tolerated sin, and Jesus cautioned against “the leaven of the Pharisees,” meaning their pervasive hypocrisy and false teaching.

Yet Jesus also used leaven positively — the kingdom of heaven is like leaven a woman hid in meal “till the whole was leavened,” picturing its quiet, unstoppable spread. The lesson cuts both ways: influences are rarely neutral and never stay contained, so it matters greatly which leaven we let in.