My greatness is directly related to my humility as a servant to all.
 It shall not be so among you. But whoever would be great among you must be your servant,  and whoever would be first among you must be your slave,  even as the Son of Man came not to be served but to serve, and to give his life as a ransom for many." - Matthew 20
 At that time the disciples came to Jesus, saying, “Who is the greatest in the kingdom of heaven?”  And calling to him a child, he put him in the midst of them  and said, “Truly, I say to you, unless you turn and become like children, you will never enter the kingdom of heaven.  Whoever humbles himself like this child is the greatest in the kingdom of heaven. - Matthew 18
“Whoever humbles himself like this child is the greatest”. To be a child means to be humbly dependent on your parents for everything. Likewise, the greatest in Jesus' kingdom are those who depend on God the most.
Am I more like a prideful, self-reliant teenager than a humble child? “Dad, help me”; “Dad pick me up”; “Dad I’m lost”; “Dad…”. Do I depend on God now like I once depended on my dad as a 5-year-old? I should. This is the path to greatness in God’s eyes.
“If anyone would be first, he must be last of all, and servant to all” Mark 9
This is not to say that being first is bad, but that those who desire to be first are often those least worthy of the position (Matthew Poole). Christians should desire to be last, regardless of their actual position, and God will exalt us according to His purposes.
To be like a child in this context is to not care about the ambition, the desiring of top positions, that pervades this world. Everybody is desiring to be first. Everyone wants to move up the corporate ladder, even in churches. And yet, Jesus is our example. He moved down the ladder. He sought out the roles that were only for servants. He considered other’s needs as more urgent and worthy of this time than His own needs. We consistently gave up His free time to love others. He was a servant to all.