Leaven in scripture is always a symbol of evil, and often of evil doctrine as well; e.g. "beware of the leaven of the Pharisees and of the Sadducees" (Matt. 16:6). As in physical baking, leaven is characterized by its infesting and spreading character. Yeast works in this way to create evenly spaced bubbles in bread. The Church is warned twice that evil must be judged, or the whole will be corrupted; in 1 Cor. 5:6 it is in connection with moral evil, and in Gal. 5:9 in connection with doctrinal evil.
- The “leaven of the Pharisees” is hypocrisy especially connected with ritualism (Matt. 16:5-12; Mark 8:15; Luke 12:1)
- The “leaven of Herod” or the Herodians is worldliness (Mark 8:15)
- The leaven of the Corinthians is immorality (1 Cor. 5:6-8). There is “the old leaven” or sexual sin, and there is “the leaven of malice and wickedness” which is on contrast with “the unleavened bread of sincerity and truth”.
Three have to do with doctrinal issues:
- The “leaven of the Sadducees” is skepticism connected with rationalism (Matt. 16:5-12). The Sadducees denied the resurrection, the existence of angels, and other truths.
- The leaven of the Galatians is legalism (Gal. 5:9)
- The leaven of the Kingdom is evil doctrine officially taught by the Church (Matt. 13:33)