Leviticus 2:11 instructs the Israelites to present their grain offerings without leaven. Yeast, or leaven, is a powerful fungus that can cause a lump of dough to rise into bread, ferment liquids into alcohol, or cause painful infections. When Jesus spoke of yeast in His comments about the Pharisees and Herod (v. 15), His disciples were quite confused.

What could He mean? What was the leaven of the Pharisees and Herod? Clearly, Jesus was warning His followers against the insidious infection of doubt. Like yeast in dough, a lack of faith can permeate one’s life until it breaks out in open rebellion against God. It was doubt about God’s good intentions towards them that led Adam and Even to sin. It started with doubt.
None of us knows what dangers or temptations lay ahead for our faith. We may be headed for trials and challenges that we never imagined. Is our faith ready to meet whatever challenges come our way? Or have we let the yeast of unbelief gain a foothold, breaking down our trust in God and spreading resistance to Him throughout our life?
An anonymous author wrote this poem:

Shall I doubt my Father’s mercy?
Shall I think of death as doom,
or the stepping o’er the threshold
to a bigger, brighter room?

Our offerings must be without doubt!