(Note: Having made a fresh study of this passage, my explanation will be different from what I’ve published in the past.)
The passage begins with precisely the question this whole series has been addressing: Who shall enter into the Eternal Age ushered in by the Messiah? The fellow was being polite and addressed Jesus as Good Rabbi. As near as anyone can tell, Jesus’ immediate response was meant to be thought provoking. It seems to suggest the man shouldn’t call someone “good” in that sense unless they represent the only One who is actually “good” — the God who defines goodness.
So Jesus then goes on to state the obvious: Keep the Law of Moses. Matthew’s choice of Greek here draws the image of someone who stands by ready to protect the Covenant from violence, to guard it and keep it safe and whole. To this the man further asks what precisely Jesus referred to. So Jesus listed five of the Ten Commandments, and finished with a generality that summed up most of them: Love your neighbor as yourself.
The man insisted that he had obeyed that from his youth; he was a good Jewish boy since at least his bar Mitzvah. Is there something more? What does Jesus require that every sincere Jew didn’t already have? It was obvious Jesus was pushing for something not already covered by standard rabbinical teaching.
Jesus had no intention of putting this man off. He gave a blunt answer that was as much a challenge as a demand: Free yourself from your attachment to worldly wealth and come follow Me. Whatever else it meant, this fellow could not have found what he was seeking in his present situation. He would need to invest a lot of time learning from Jesus like the other disciples. I’m convinced this was an invitation to join the crew, because it sounded like he was quite serious about this.
But the answer stunned him, as he was quite wealthy. He just wasn’t ready to let it all go. Some part of him was still chained to the old ways he thought he was ready to abandon. He turned away with a heavy heart, so close and yet so far. We can be sure Jesus was moved by this, as well. He turned to His disciples and noted something that is poorly understood outside Judean society. It’s extremely difficult for rich people to let go of all their advantages in this life and focus on eternity. Then Jesus cites imagery from Jewish oral tradition that is roughly equivalent to “as much faith as a mustard seed.” Old commentary on the Hebrew Scripture suggests that God says in so many words, “Open to Me so much as the eye of a needle, and I’ll drive through it tents and camels.”
It’s possible the Twelve were not familiar with that saying, but taking a cue from Matthew’s choice of words, the image itself would sound like regular Hebrew hyperbole, since the camel was the largest land animal anyone in Palestine saw. It basically meant it was impossible. The reason they were so shocked is that they had been taught their whole lives that material wealth among Jews was the primary sign of God’s favor. If those whom God seemed to favor most weren’t actually going to make it into the Messiah’s eternal kingdom, just who could?
Jesus stuck to the point of his parabolic image: Nobody could by their own abilities. It requires a miracle of God. The rich young man didn’t receive his miracle, but the disciples were reminded that they had sacrificed much on their own terms to be with Jesus. Maybe nothing like the rich young man, but it was all they had. Jesus affirmed that this was the sacrifice necessary in this life to see eternal life.
Then Jesus cited a favorite saying of His, that the Kingdom of Heaven stood on its head a great many things people were so sure about in this life. It was more than a puzzling paradox of truth; it was a warning to be ready for many shocking reversals from what everyone assumed.