Can you imagine how the disciples felt as they came down from the mountain? Imagine the high of seeing Jesus in his glory. What will happen now, surely it will be glory all the way. But when they get down the mountain they are brought down to earth with a bump. The next section of incidents are almost a montage of the disciples failures.
In the first incident, the big question in v41 is who is Jesus speaking to the crowd or the disciples? Who does he rebuke and why? I wonder if Jesus is addressing both the crowd and the disciples. The disciples have manifested their lack of faith in their failure to cast out this evil spirit, but Jesus will once again show them his glory, what they cannot do he will do. It is Jesus glory that this incident shows to the amazement of the crowd. Jesus is God revealing his glory.
Whilst they are still thinking about this incident Jesus teaches them that his glory will be made most manifest as he goes to the cross (v44). Luke emphasises that the disciples do not understand what Jesus is saying in both verse 45 and the incident following as the disciples argue over who is the greatest. As Jesus reveals that he is God made man in all his glory and that he will go to the cross, the disciples are arguing about which of them is the greatest. Jesus uses an object lesson as he stands a little child in front of them. Greatness in the kingdom is dramatically different, it is achieved through humility and serving of others.
But it will face opposition. Jesus knows and experiences that as he goes through a Samaritan village on his way to Jerusalem. The people reject him because of where he is going, he is determined to reach Jerusalem even knowing what it means for him. Yet again we see the disciples wrong reactions, as James and John ask if they should call down destruction on the city. They are right in one sense that rejection of Jesus is grounds enough for judgement, but they are swift to judge unlike Jesus, who rebukes them.
Finally Jesus teaches them about the cost of following him. It is hard not easy or comfortable. It makes Jesus the disciples number one priority, anything less is to fail to really grasp who he is.
The various pictures we are given of the disciples here show us how much they have yet to grasp about who Jesus is and what it means to follow him. But above all they serve to highlight the grace of Jesus, he will go to the cross to die for his followers, including these men. Grace is the reason we relate to God rightly not our record and that will always be the case. Don't be quick to look down on the disciples rather take time to identify with them.