Watch out for the yeast of the Pharisees and that of Herod

Mark 8:11-26
The Pharisees came and began to question Jesus. To test him, they asked him for a sign from heaven. He sighed deeply, "Why does this generation ask for a sign? Truely I tell you, no sign will be given to it."
Be careful, Jesus warned them,"Watch out for the yeast of the Pharisees and that of Herod.";
Jesus heals a blind man at Bethsaida.
The disciples lack of spiritual discernment disappoints Jesus. They are so taken up with the bread-supply, they cannot see that he is warning them against the ever present dangers of religious hypocrisy and materialism(the prime concern of the pro-Herod faction).
This story 'match' that of the deaf man; so with the coming of God's kingdom the blind see and the deaf hear, as Isaiah had predicted. But still Jesus guards against publicity.
The story can also be taken as a 'frame' to the section that follows, and which closes with the healing of another blind man.
Why?
Why does this generation ask for a sign?  They do not believe the word and what Jesus done among them.
The yeast among people's heart may produce many evil things. Yeast can stand for “deceptive teaching”. Like actual yeast, the false teaching and false living of the Pharisees can impact all of life.
Herod was obviously impressed by Jesus, yet he did not believe in him or his message of the kingdom of God.
How?
So help me, Lord, to avoid the “yeast” of the Pharisees and Herod. Help me to trust you more deeply and consistently, both with the biggest things and with the small ones. Amen.