In the wake of the previous passage (feeding of the 4,000), there was a continuing discussion on bread. Jesus warned the disciples about the “yeast of the Pharisees and that of Herod” (Mark 8:15). Clueless as to what He meant, the disciples discussed among themselves and decided He was talking about their present lack of bread (v. 16).

Jesus seemed exasperated by their lack of understanding—what a bunch of dim-witted disciples! “Do you still not see or understand? Are your hearts hardened?” (v. 17). Jesus remarked sadly that they had unseeing eyes and unhearing ears (v. 18). He then reminded them about the two miracles of feeding the crowds (vv. 19–20). In each case, He asked them how many baskets of leftover pieces they had collected. Their answer was arithmetically correct but the significance still eluded them. Further exasperated, Jesus asked them: “Do you still not understand?” (v. 21).

What did the disciples fail to understand? When Jesus mentioned yeast, they should have remembered the trick of mixing a pinch of old, yeast-rich dough in with a new batch to help it rise. While this was a helpful practice in the kitchen, Jesus was using it as an illustration, to point out the harmful effects of putting the “old dough” of the Pharisees into the new teaching of Jesus. Here, yeast was being used by Jesus to represent the sinfulness of the human heart, which was abundantly found in the false piety of the Pharisees. They had totally misunderstood the nature of the kingdom of God and considered it only in terms of power and ritual.

The Herodians were even worse, focusing on political power and expediency. These were dangerous and pervasive influences. Jesus warned the disciples against ever giving ear to these false versions of the gospel.

But the disciples were so focused on their lack of physical bread that spiritual lessons from the Master degenerated into materialistic concerns in their hearts. The key words are “forgotten” (v. 14) and “remember” (v. 18). The disciples forgot to bring bread for the journey—that was their carelessness. But they also failed to remember the lesson of the feeding miracles—that Jesus who fed crowds would have no problem feeding His disciples. They should have trusted Jesus and listened to the deep spiritual truths He was teaching. They were forgetful and distracted students, and slow to understand.