11. (a) In Bible times, what was leaven, and what effect does it have? (b) In the Scriptures, how is leaven used figuratively? Illustrate.

¹¹ Leaven, in Bible times, was a piece of sour dough that had been preserved and that was added to a new batch of dough to make it ferment and form gas bubbles that would leaven or lighten the whole mass. The fermentation is really a breaking-down process, a corrupting, so that it often causes spoilage. For this reason it is generally used in the Holy Scriptures in a bad way figuratively. For instance, the unbelieving Pharisees and Sadducees were purveyors of spiritual leaven, regarding which Jesus told his disciples: “Watch out for the leaven of the Pharisees and Sadducees.” The disciples grasped this to mean the “teaching of the Pharisees and Sadducees.” (Matthew 16:6-12) According to Luke 12:1, Jesus told his disciples: “Watch out for the leaven of the Pharisees, which is hypocrisy.” This doctrinal and ritualistic leaven could also have a political tinge, as represented by the Jewish party followers of King Herod; so that Jesus said: “Keep your eyes open, look out for the leaven of the Pharisees and the leaven of Herod.”​—Mark 8:15.

12. In 1 Corinthians 5:6-8, leaven was used to represent what, and in contrast with what?

¹² Fully in obedience to that warning, the first-century Christians were celebrating in their daily lives the antitype of the ancient Jewish festival of unleavened bread or cakes, the festival that was celebrated for seven days after the annual Passover. Quite appropriately, then, the apostle Paul warned them against the figurative leaven, saying: “Your cause for boasting is not fine. Do you not know that a little leaven ferments the whole lump? Clear away the old leaven, that you may be a new lump, according as you are free from ferment. For, indeed, Christ our passover has been sacrificed. Consequently let us keep the festival, not with old leaven, neither with leaven of badness and wickedness, but with unfermented cakes of sincerity and truth.” (1 Corinthians 5:6-8) This statement of the apostle contrasted the figurative leaven of badness and wickedness, false sectarian teaching and religious hypocrisy, with sincerity, genuineness and truth.

14, 15. (a) What effect does figurative leaven have on a religious organization? (b) With what language did the apostle Peter warn against such an influence in the congregation?

¹⁴ Like literal leaven or yeast, figurative leaven causes a souring of a religious organization. It is an agency that corrupts religiously. It is prepared by Satan the Devil, and he uses earthly human agents to introduce the figurative leaven into a clean religious organization with the design of corrupting it and making it unfit for God’s use and making it a reproach or discredit to God.