Jamieson, Fausset and Brown on Mark 8:21

21. How is it that ye do not understand?--"do not understand that the warning I gave you could not have been prompted by any such petty consideration as the want of loaves in your scrip." Profuse as were our Lord's miracles, we see from this that they were not wrought at random, but that He carefully noted their minutest details, and desired that this should be done by those who witnessed, as doubtless by all who read the record of them. Even the different kind of baskets used at the two miraculous feedings, so carefully noted in the two narratives, are here also referred to; the one smaller, of which there were twelve, the other much larger, of which there were seven.

Blind Man at Bethsaida Restored to Sight (Mr 8:22-26).