And Jesus said to them, “See and beware of the leaven of the Pharisees and Sadducees”.
Jesus warns the disciples, using the word “leaven” as a symbol, which in Jewish tradition sometimes represents corruption or a sinful influence. Here it symbolizes the false teaching, hypocrisy, and misleading conduct of the Pharisees and Sadducees. Jesus points out that even teaching that appears outwardly pious, if it is distorted, can gradually undermine the whole faith, just as leaven spreads through leavened bread. The disciples at first understand it literally, but Jesus will soon explain its spiritual reality. This is an important lesson: always be watchful and discerning, even toward the words of religious authorities.