(Latin: levare, to raise)
Any substance acting or used to produce fermentation as in dough or liquids; anything which makes a general assimilating change in a mass or aggregate, or which modifies or tempers the whole. In the great solemnity of the Passover the Jews were bidden to eat unleavened bread (Exodus 12,13, 34; Numbers 12; Deuteronomy 16). This was a symbol of sinlessness. Saint Paul applies this symbolism to the state of righteousness in the Christian code (1 Corinthians 5); Our Lord employs leaven as a symbol of sin (Matthew 16; Mark 8); and the imperceptible penetrating efficacy of the Gospel of Christ is compared to leaven (Matthew 13; Luke 13).