"At this the man's face fell. He went away sad, because he had great wealth." NIV translation
When faced with the decision to trust in his material wealth or to trust in Jesus, the man chose his wealth. This is what Jesus was talking about when He described the cost of being a disciple (see Luke 14). If you put your hope and trust in anything but the finished work of Jesus Christ, then, you do not have faith in Jesus. Without faith, it is impossible to please God and you are lost.
"Jesus looked around and said to his disciples, 'How hard is it for the rich to enter the kingdom of God!' The disciples were amazed at his words. But Jesus said again, 'Children, how hard it is to enter the kingdom of God! It is easier for a camel to go through the eye of a needle than for someone who is rich to enter the kingdom of God.'" NIV translation
Jesus repeated Himself and explained how difficult it was for the rich to give up their self reliance and to trust in Him. He calls them "children" as they were still at the beginning of their understanding of the ways of God. The camel was the largest animal in the land and the eye of the needle was the smallest of openings. He used this contrast in sizes to see how it was impossible under human strength. No matter how hard you tried or how much time you spent in it, you were not going to be able to push a camel through that opening.
"The disciples were even more amazed, and said to each other, 'Who then can be saved?' Jesus looked at them and said, 'With man this is impossible, but not with God; all things are possible with God.'" NIV translation
The disciples were puzzled because they were all from humble beginnings. They were not used to the fact that it was easier for them to do something than a rich man who could easily hire someone to do his work. Jesus went on to explain that it is faith that saves and not the works of men.