While Jesus and His inner circle were up on the mountain, the rest of the disciples were staying in the town at it’s base. When they return, they find a crowd waiting for them. From the crowd, a distraught father begs Jesus to help his son because the disciples weren’t able to cast out the spirit that afflicts him.
In response, Jesus expresses some frustration, which is a really weird thing to think about. It’s not an emotion that feels…comfortable…to assign to the Sovereign Lord of all. But it is there in the text, and we have to deal with it as it is, and not as we’d like it or expect it to be. The question appears to be directed more at the crowd, or perhaps at the disciples, than at the father. All of these people have heard Jesus’s teachings, but do not believe God’s power is sufficient or necessary for their lives. Or something.
Jesus tells them to bring the man’s son to Him so that he can be healed. The boy has one last fit along the way, but Jesus casts out the spirit and all the people are “astonished”. (v. 43) Were they astonished because they didn’t really believe that the boy could be healed? That he was healed because all Jesus did was rebuke the demon causing the problems? What were they expecting? If this was their attitude, then Jesus’s frustration is a bit more understandable.
Immediately after this, Jesus plainly tells His disciples that He is going to be arrested, at the very least. But they don’t understand what He means because God hides it from them until the proper time. Jesus needed no interference from well-meaning friends so that the plan of redemption would be completed as it should.
Let us always take Your word for what it is and not try to twist it into something it does not say.