Self-interest always produces arguments (or unexpressed resentment, bitterness and frustration).  Perhaps Jesus' selection of Peter, James and John to join Him at the recent transfiguration (Luke 9:28) might have triggered this ugly ego-surge.  Although Jesus was not present when the argument broke out between the disciples, He knew all about it.  So, at a convenient moment, He used a child to demonstrate the principles by which His Kingdom operated.  Those values would turn worldly standards upside down: or more correctly - the way of the world has so corrupted God's way, that we need God's truth to turn us the right way up.

In putting the child next to Him, Jesus was not saying that we should worship children, or that children are angels who are able to usher us into God's presence!      He was simply making the point that children are willing to receive love, but true love is costly, as every parent knows.  Jesus welcomed children and honoured their trust in Him, and the disciples should do the same.  And if they were willing to honour a little child, then they should honour each other by providing whatever kindness was required.  Greatness, according to Jesus, is not marked by power but by service, particularly to those who do not appear to deserve it.

Jesus said, ‘Anyone who wants to be first must be the very last, and the servant of all’ (Mark 9:35); and a ‘slave of all’ (Mark 10:44).  The greatest in God’s kingdom is the person who serves sacrificially, not seeking honour and being willing to suffer unjustly (1 Peter 2:20-23).  Jesus provided the greatest example. He served and honoured us, unworthy sinners, by obeying Father God in unjustly suffering for us on the cross (1 Peter 3:18).   

In that perspective, all ideas of power struggles amongst believers are quite out of order.  Nobody has any right to claim superiority over others when our Master humbled Himself to the point of death (Philippians 2:5-8). The principle still stands - greatness is measured in sacrificial service.  So, one of the best ways of showing friends and colleagues what following Christ means, is to be humble enough to serve them and even to serve those people whom they despise.