HE disciples asked two questions of Christ, which Matthew recorded for us in this chapter (Matthew 18:1& 21). In both cases Jesus attempted to guide them toward humility.
First off, when the disciples asked about who would be great in the kingdom, Jesus introduced them to a little child. "Be like this kid!" was His answer. And, He wasn't being smart-alecky. He sincerely desired to see them humble themselves. He knew that humility was exactly what they needed. He knew how the Father resists pride and accepts humility (James 4:6).
Then Peter asked Christ just how humble we must be. Of course, a spiritual limbo dance of "how-low-canyou-go?" is counter-productive. A man who attains genuine humility & exudes godly forgiveness will not be concerned with how many times he has forgiven others. So, Jesus presented a parable in which there was a servant who had been forgiven a great debt, yet he was unwilling to forgive one of his fellow servants a small debt. The point is that since we have been forgiven of so very much, we should tend toward mercy in every direction. To do otherwise is to be controlled by and to act with evil pride.