A) Jesus promptly dismantles their theology. He calls a small child to Him, placing the child among them. He then delivers a stark truth: unless they repent and become like a little child, they will not enter the Kingdom of Heaven. This is a profound way of saying that their quest for greatness is sinful.

B) The problem is straightforward. The disciples needed to repent because they were trying to figure out who was the greatest among them in the framework of ministry. Therein lies the problem. People who try to become the greatest in ministry need to repent because that's not the goal of ministry. The ministry is to serve one another and honor Jesus Christ. Jeremiah 45:5 says, do not seek greatness for yourself.