LEAVEN, sourdough starter — and the thing Passover requires be actively hunted out of the house: 'seven days no LEAVEN shall be found in your houses' (Exodus 12:19). Its force as an image is that it works invisibly and spreads through everything, which is why it becomes a metaphor for corruption that cannot be quarantined — 'a little LEAVEN leavens the whole lump' (1 Corinthians 5:6, where Paul goes straight on to call Christ our Passover), and 'beware of the LEAVEN of the Pharisees' (Matthew 16:6). ⚠️ It is not always negative: Jesus also likens the kingdom of the heavens to leaven a woman hides in three measures of flour until the whole is leavened (Matthew 13:33) — the same property, working the other way. ⚠ The grain-offering law states the flood-gate version of the same rule outright: no leaven, and no honey either, may ever be turned into smoke on the altar — not just at Passover, but from EVERY offering, without exception (Leviticus 2:11, already on these pages). → first discussed at Exod 12:15