In the middle of the passage the disciple begin to argue about who will be the greatest in the coming kingdom. Jesus knowing their hearts pulls up a small child and reminds the disciples that his kingdom is made of such. We are not to be fervent self-seekers, but rather ardent givers. We are to put others ahead of ourselves. In this way the first will be last and the last will be first. In essence everyone serves and gives to their ability, for God is not interested in what we have to bring him, but what he has to give us.
Sometimes we can fall into the pit of bitterness by thinking God owes us favor or respect over others. The truth is that we owe God more than we could ever pay for our salvation. To be part of hHis kingdom is reward in itself and to see others come into the kingdom and encourage one another along the way ought to be enough.