T. Austin-Sparks emphasizes the dual interpretations of the parable of the leaven in Matthew 13:33, arguing that leaven symbolizes evil rather than good. He explains that throughout the Bible, leaven is consistently associated with corruption and that the presence of evil will proliferate in the world until the return of Christ. Sparks warns against the dangers of hypocrisy, materialism, and superficiality, urging believers to remain pure and separate from the leaven of the world. He concludes that while evil may abound, the faithful must strive to be unleavened bread, pleasing to God, as the Kingdom of Heaven will ultimately divide the good from the evil.