Mark 8:21

“And he said unto them, etc..] Since this was the case, and they so well remembered the miracles he had wrought, and the circumstances of them: how is it that ye do not understand? my words concerning the leaven of the Pharisees, of the Sadducees, and of Herod, as to imagine I spoke of bread, taken in a literal sense; or that I concerned myself about the scantiness of your provisions, when you, might have learnt from my late miracles, how able I am to support you, if you had not so much as one loaf with you: wherefore it argues great want both of understanding and faith, and shows great stupidity, ignorance, and unbelief, to give such a sense of my words, and to be anxiously concerned on the…”

“See this passage explained in Matthew 16:1-12. Mark 8:12 Sighed deeply in his spirit - His heart was deeply affected at their wickedness and hypocrisy. The word “spirit” here is taken as the seat of the emotions, passions, affections. He drew groans deeply from his breast. No sign be given - That is, no such sign as they asked, to wit, a sign “from heaven.” He said a sign should be given, the same as was furnished by Jonas, Matthew 16:4. But this was not what they “asked,” nor would it be given “because” they asked it. Mark 8:15 Beware of the leaven of the Pharisees - See Matthew 16:6. Of Herod - Of the Herodians - of Herod and his followers. Matthew, instead of “Herod,” has “the Sadducees.”…”

“8:21 Don’t you understand yet? This question implies a time when they would truly understand. Mark’s readers knew that Jesus’ resurrection would give the disciples understanding of Jesus’ identity and power (see, e.g., Acts 4:23-31).”

“How: Mar 8:12, Mar 8:17, Mar 6:52, Mar 9:19; Psa 94:8; Mat 16:11, Mat 16:12; Joh 14:9; Co1 6:5, Co1 15:34 Mark 8:22”