John Gill Commentary Mark 8:21

"And he said unto them, Do ye not yet understand?" — Mark 8:21 (ASV)

And he said to them
Since this was the case, and they so well remembered the miracles he had wrought, and the circumstances of them:

how is it that you 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 score of your provisions.