Theophylact of Ohrid — as excerpted in the Catena Aurea on Mark 8:10-21

“But the disciples themselves thought that the Lord spoke of the leaven of bread. Wherefore it goes on, And they reasoned amongst themselves, saying, it is because we have no bread; and this they said, as not understanding the power of Christ, who could make bread out of nothing; wherefore the Lord reproves them; for there follows, And when Jesus knew it, he said unto them, Why reason ye because ye have no bread?”