Whosoever therefore shall humble himself as this little child, the same is greatest in the Kingdom of heaven.
Matthew 18 v 4
The most desired status human crave is to be great. We all try to achieve greatness in different ways.
As a child I was shy but inwardly I wanted to be above my school mates so when they were playing and having fun I was serious and studying. The result was I came first occasionally second in my class at all times. In those days pupils did exams almost every week and we were promoted according to ability not age, so at a very young age I got to the highest standard in school. I remembered my parents being very proud and I was proud of myself but I did not know it was sin. I grew up in an environment where, if a family had more than another the less well off one will be exploited and looked upon like if they were nothing. This was a class system that created a division among the people where some felt they were better than others and as children we were not allowed to mix with those that are not of our class/group. Obviously children are trained into mind sets that would determine the pattern the adult should follow, however within us human we have a second person/nature that tells us something is missing/wrong. Some of us work towards becoming great; for example Leaders, celebrities, professionals, millionaires and so on. With this greatness a pride that one is better than another and would more or less would look down on others.
The divisive communities created these days are the haven for pride that causes the turmoil in our nation and world currently.
Here Jesus is saying unless we become as a child, that is being like a child. (We know what a child is, it is an inocent being not able to think or do things on it own, it depends upon its parents) we cannot enter the Kingdom of heaven. Again Jesus is/was talking spiritually and he means we have to be prideless dependant on Him then we enjoy greatness. Greatness means we are composed, peaceful and contented.
When we are in this state of mind we are in heaven on earth and the turmoil around us will not affect our lives. This I believe Jesus means our mind set becomes higher than the earthly mind set, therefore, we are above in heaven or the kingdom of heaven, then our real greatness could be seen and enjoyed by all people in the world.