They began to discuss with one another the fact that they had no bread. Mark 8:16
The disciples have just witnessed Jesus feed 4,000 people with 7 loaves of bread, however when they were leaving they forgot to bring the leftover bread (7 baskets) with them on their next journey.
Instead of marveling over the miracle they just witnessed, they continued to focus on the fact they only had 1 loaf of bread for all of them to share.
And Jesus, aware of this, said to them, “Why do you discuss the fact that you have no bread? Do you not yet see or understand? Do you have a hardened heart? Mark 8:17
Jesus is perplexed how these men could witness all of these miracles and listen to tall his teachings, yet no apply it to their lives. God just demonstrated that he would provide by feeding 4,000 people with 7 loaves, however the disciples are worrying about their lack of food
We are like the disciples also, we know all the stories about the miracles of Jesus. We know all the promises from God throughout the Bible, yet we worry about our basic needs, our hearts have been hardened
when I broke the five loaves for the five thousand, how many baskets full of broken pieces you picked up?” They said to Him, “Twelve.” “When I broke the seven for the four thousand, how many large baskets full of broken pieces did you pick up?” And they said to Him, “Seven.” And He was saying to them, “Do you not yet understand?” Mark 8:19-21
Jesus is reminding them of the miracles that they have witnessed, the feeding of the 5,000 and the 4,000. Jesus asks them “Do you not yet understand”? Do we still not understand that nothing is impossible for God? Do we still not understand God will provide for all our needs? Don’t allow your heart to be hardened to Jesus Amen!