Christian spirituality: They understood that he did not say to beware of the yeast used in bread, but of the teaching of the Pharisees and Sadducees. Matthew 16:12

The Gospel of Saint Matthew relates that Jesus, while in the region of Galilee, performed, in similarity to the prophet Elisha, the miracle of the multiplication of the loaves. With this miracle, Jesus was presenting himself to both pagans and Jews as a new manna come down from heaven to feed a new Israel, not according to the flesh but according to the spirit. But also occurred that a new spiritual doctrine, the doctrine of the Kingdom of God, announced by Jesus, aroused great curiosity among the people, and so, just as some admired Jesus, others envied him, and many wondered who he really was.
But everything Jesus had done—preaching a new spiritual kingdom and performing miracles—had brought him dangerous enemies. The Sadducees and Pharisees had conspired among themselves to physically eliminate Jesus because he was a problem.
And it happened that the enemies of Jesus asked him to make a sign in the sky, and Jesus prophesied unto them that they would receive the sign of Jonah, referring to his resurrection on the third day. Some time later, Jesus turned to his disciples and said the following words: "Be on your guard against the yeast of the Pharisees and Sadducees" Matthew 16:6. But the disciples did not know how to correctly interpret Jesus' words, and thought that he meant that they had not brought bread with them, and Jesus rebuked them.
The gospel recounts that the disciples finally understood the words of their master: "They understood that he did not say to beware of the yeast used in bread, but of the teaching of the Pharisees and Sadducees" Matthew 16:12. For Jesus, the yeast according to his teachings was what made men's thoughts "ferment," and just as there was a benevolent and edifying yeast, the yeast of the Kingdom of God, there was a chaotic, destructive, and unjust yeast, the yeast of God's enemies. These teachings must be understood in the context of the Christian spirituality in the sense that faith begins with hearing the word in order to practice it; the good leaven, like the seed that falls on the ground to be sown, is then essential to redeem and free men from the slavery of sin as Jesus taught.

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