The apostles are making some progress. They still have a distance to go, as is clear from what follows, but it is impressive that, when Jesus told them that he was going to Jerusalem to be mocked, to be spit upon, to be scourged, and put to death, James and John ask to be given positions of prominence in his kingdom. It is not clear that they understood totally what it would mean to drink the chalice that Jesus would drink and be baptized with his baptism, but they were eager to bet everything they had on Jesus, no matter what. Some of the crowd following Jesus to Jerusalem, a motley group of the poor and lower-class with a few wealthy women mixed in, without weapons, might have been doubting the whole enterprise; James and John see the same group, with Jesus at the head, and just want to make sure that they have a good position locked up in the kingdom that would inevitably result.
They displayed great faith, but something was still missing, and their question becomes an opportunity for us all to learn something about what it means to be great. James and John were not unwilling to do the hard work: they were following Jesus, even to be spit upon and scourged. They merely wanted to be sure of the reward at the end. They wanted to be something great, and, thinking with minds of this world, they asked for a position of greatness. Jesus told them, and us, that the positions of greatness in the Kingdom of God are not merely handed out as rewards.
Jesus is telling us that, in the world, the weaker serve the stronger, because the stronger are able to force the weaker to do so, but in the Kingdom of God, the stronger serve the weaker, because they are the ones able to serve. This is simply one way that our world has gotten things completely backward. The strong man should carry the weak man, but we expect the weak to carry the strong. In the Kingdom, we serve our brothers and sisters who are in need; the angels, who are stronger and smarter than us, serve us; and God, who is infinitely strong, serves all of us. If we want to be great, we need to do great things: we should find someone who needs our help, and then help them.