Jesus is the Messiah whose life, death, and resurrection are God's saving act for humanity instructs his disciples on true greatness in the kingdom. Greatness in the kingdom depends on having the humility of a child and welcoming such “little ones.”
Rather than being the topic of an argument among themselves as in Mark (Mark 9:33 34), the disciples in A tax collector who became one of Jesus' 12 disciples come appropriately to Jesus with their questions about who is greatest in the kingdom. Jesus responds that entrance into the kingdom depends on having the humility of a child, and greatness in the kingdom means to have the kind of hospitality that recognizes and welcomes such little ones. The consistent use of children and “little ones” to describe the members of the kingdom marks a pointed contrast to the disciples’ question about greatness (see also 19:13-15).
The opposite of such welcoming of “little ones” is treated in 18:6-9. The word variously translated as “stumbling block” or “temptation to sin” is the same word that is translated as “offense” in Matthew 11:6 and links these passages around the theme of following Jesus. The stumbling block refers to anything that occasions one of these “little ones who believe in me” (18:6) to be lost to the kingdom. Exaggerated language describes the seriousness of rooting out any defect that would get in the way of anyone’s belonging to the kingdom. This is serious business, but serious especially for those who fail to hold fast the little ones.