This pericope parallels and recalls Jesus' teaching about bread when He cast the demon out of the Phoenician girl (7:24-30). In both cases leavened bread metaphorically represented teaching. The Gentile woman wanted Jesus' teaching and so presented a positive example for the disciples. The Jewish religious leaders rejected Jesus' teaching and advanced false teaching, which Jesus warned His disciples to avoid.
8:14 The one loaf of bread also recalls the two miraculous feedings of multitudes. A shortage of bread should have been no great concern to the disciples in view of Jesus' supernatural powers.
8:15 Jesus evidently used the leaven in the loaf of bread as an object lesson to illustrate the pervasive corrupting teaching of the Pharisees and of Herod. The teaching of the Pharisees was that Jesus received His authority from Satan rather than from God (3:22; cf. 7:8-13). It was a denial of His role as God's anointed Servant, Messiah. The teaching of Herod Antipas, what he believed and articulated, was likewise that Jesus was not the Messiah. Herod told others that Jesus was just John the Baptist come back to life (6:14-16). The Pharisees and Herod, though so different from each other in many respects, promoted the same heretical view that Jesus was not the Messiah, much less divine.193
8:16 The disciples' interest in the problem of lack of food contrasts with Jesus' fervent concern over unbelief (cf. vv. 12, 15). Spiritual truth failed to impress them because they had minds that were not open to it (v. 17).
8:17-21 Jesus strongly rebuked His disciples for their lack of spiritual understanding. In view of the two miraculous feedings they had witnessed, they should have understood who He was. As God had provided bread abundantly for the Israelites in the wilderness, Jesus had provided bread abundantly for them in another wilderness. The conclusion should have been obvious. Jesus was the prophet that Moses predicted would follow him and supersede him. He was the divine Messiah.
"His rebuke was not because of their failure to grasp the meaning of His warning (v. 15), but at their failure to understand the meaning of His presence with them."194
It was extremely important that the disciples perceive who Jesus is. Without that perception they could not serve Jesus as the apostles He needed. Jesus' use of questions forced them to interact with the implications of what they had heard and seen.
The incident ends with a question but no answer. Mark leaves the reader hanging. The answer is of utmost importance. Peter finally verbalized it in verse 29.
