In this scripture many things come out. First, let us start with verse 18, " No one is good except God alone". Jesus was a pure sacrifice who was blameless and without sin. He himself asked why he was being called good if no one is good but God. That verse is something to ponder on.
Verse 21 it mentions that Jesus looked at the man who stated that he has done all of what Jesus has asked. Jesus looks at him in love knowing that he has not. So many believers stay to Jesus I have done all that you asked of me nut there is always that one or two things that they are not willing to surrender to him. Surrendering to Jesus is giving him all we are and have and trusting him to put it together on our behalf if that is the Fathers will for us. Just withholding nothing from him. So many become dishearten with Jesus because they refuse to surrender all of who they are to him.
Verse 27 states "With man it is impossible, but not with God. For all things are possible with God." This reminds me of how often we look to man to make things possible for us then become disappointed when it does not become. The scripture is teaching the disciples something do not go to man first for anything you are in need of but to the father where everything is possible. Making it a pattern to go to man first will weaken your faith in God because the choice to ask man first is out of order according to this scripture.