Matthew 16:1-12
In this passage Jesus rebukes both the Pharisees and Sadducees, and later on his own disciples, for their unbelief. Jesus scolds both groups for not knowing better: the religious leaders for not knowing how to read the sign of the times, and the disciples for fretting about bread on the heels of his two feeding miracles. One group is openly hostile toward Jesus, and the other are his friends. So what is the difference between the unbelief of the two groups? The first group Jesus would later refer to as sons of hell (23:15). The second group Jesus ends up commissioning to preach the gospel to all the world, even as they stand there doubting his resurrection (28:16-20). So how do we know if we have an unbelieving unbelief or a believing struggle with unbelief? How can we know if Jesus is going to respond to us with scary condemnation or with a fatherly scolding?When the Pharisees and Sadducees asked Jesus for a sign, they did so because they were "testing him." It wasn't the first time either. The Pharisees along with the scribes had made it a practice to stalk and harass Jesus regularly. Back in 12:38-42 they demanded a sign from him and were denied. Jesus told them then that the only sign they would be getting was the sign of Jonah, and even gave a lengthy explanation of what that meant. So you can understand his curtness to them in this passage. He had been around this merry-go-round with them before. Not to mention the Pharisees were also going around publicly accusing him of casting out demons using satanic power (12:24) and were actively plotting his destruction (12:14).
So there's that history. But even aside from all that, their entire attitude toward Jesus in this encounter reeks of arrogance. "You're guilty until proven innocent." "You need to convince us on our terms, not yours." All the while pretending to be seekers who wanted to know the truth, who needed only one more sign to convince them, as if Jesus' very public mass healings and feedings and exorcisms were a paltry show. They came to him with a dishonesty, insincerity, and deceitfulness that made Jesus turn around and walk away. There was an evil agenda hidden behind those smiling faces. The reason they didn't believe is quite simply because they didn't want to.
The disciples by contrast did believe. Jesus called them "you men of little faith," not "you men of no faith." They did have a weak faith, but they did not come to him deceitfully. They were anxious to do things right, so much so that they got all tied up in knots over forgetting to bring bread for the trip. They thought Jesus would be disappointed because they were irresponsible. It never occurred to them that Jesus actually expected them to be irresponsible at times, and what really disappointed him was that they didn't console themselves with the realization that he could simply provide. Apparently they thought he provided bread for the multitudes because those people were pitiable. But to provide bread for themselves because they had been forgetful was, in their minds, not a good enough reason.
This reasoning sounds familiar, doesn't it? I don't want to ask God to provide for me if I was irresponsible. I was late getting out of the house. Should I pray that the meeting would start late? But I deserve to face the consequences of my actions, not treat God as a genie to get me out of another scrape! How can this be a time for faith when it should be a time for guilt and self-flaggelation? It never occurs to me that Jesus is more disappointed in my unbelief, in my assumption that he can't (or won't) help me, than he is in my laziness or forgetfulness.
So the unbelief of the disciples was of a completely different kind than that of the Pharisees and Sadducees. It had to do with the limits that they, in their little faith, put on Jesus' love for them. Jesus' rebuke to them was in the vein of what he said back in 6:30: "But if God so arrays the grass of the field, which is alive today and tomorrow is thrown into the furnace, will He not much more do so for you, O men of little faith?" The unbelief of the Pharisees and Sadducees, on the other hand, wasn't even close to being engaged in the struggle to believe in Jesus' love for them. As far as they were concerned, Jesus had nothing to offer them. It was their job to judge him. Their unbelief was all about looking for grounds to discredit him, to ultimately drag him before the authorities and have him killed.