1 Corinthians 5:8

wherefore let us keep the feast, not with old leaven, neither with the leaven of malice and wickedness, but with the unleavened bread of sincerity and truth. [Verses 6-8 form an enlargement of verse 2. The reference to the passover was probably suggested by the season of the year (1 Corinthians 16:8), and was very apropos. Leaven is a type of evil, illustrating the hidden constant way in which it spreads. To the Jew it was a symbol of the corruption of Egypt, and he was directed just before the passover to search for it diligently in every part of his house, and remove it (Exodus 12:15). But to the Christian Christ is a perpetual sacrifice, an ever-present paschal Lamb, demanding and enforcing constant vigilance and unceasing cleanliness. The individual must put away every sinful habit of the old life. The church must purge itself of all whose lives are sources of corruption.]