What does Mark 10:23 mean?

The rich young man's issue with money is equivalent to the Pharisees' spiritual snobbery. Jesus condemns the Pharisees three times for doing something in public in order to receive public praise (Matthew 6:2; 6:5; 6:16). He explains that the praise they get by men is their only reward, and they will not receive a reward in heaven. Similarly, the rich are provided for on earth. As much as the rich young man wants eternal life, he finds it hard to "set [his] mind[] on things that are above" when the things on earth are so pleasant (Colossians 3:2). It's difficult to choose to suffer for the gospel when suffering in general is foreign to you.

Comfort in worldly things is a hard thing to give up. Even one of Jesus' disciples, Judas, falls into its trap. When Mary of Bethany anoints Jesus' feet with expensive perfume, Judas scoffs at the waste, but he is really upset because if she had donated the money, he could have stolen it (John 12:1–6). Shortly after, of course, Judas delivers Jesus to the chief priests for thirty pieces of silver (Matthew 26:14–16). Judas finds the lure of money stronger than his devotion to Jesus, and it kills him (Matthew 27:3–10). Many rich throughout history have also struggled with their love of the world.

But the struggle is not hopeless. Zacchaeus is a chief tax collector and very rich. After an encounter with Jesus, he volunteers to give away half his possessions and restore what he had defrauded people four-fold. He does so in willing submission to Jesus' authority, and Jesus responds by saying, "Today salvation has come to this house" (Luke 19:1–10). The point isn't that rich people have to give all their worldly possessions to be saved. Zacchaeus, for example, didn't give away his every penny. Rather, we should all love and follow Jesus so much that possessions are no longer foremost in our affections.