As Jesus started on his way, a man ran up to him and fell on his knees before him. "Good teacher", he asked, "what must I do to inherit eternal life?"
"Why do you call me good?" Jesus answered. "No one is good -- except God alone." ~Mark 10:17-18
Jesus is not saying that he is not good or that God the Father is the only one who is good. Jesus confronts the man's faith. If the man testifies, as he did, that Jesus is good, then by doing so, he has testified that Jesus is God. There is no alternative.
"You know the commandments: 'Do not murder, do not commit adultery, do not steal, do not give false testimony, do not defraud, honor your father and mother.'"
"Teacher," he declared, "all these I have kept since I was a boy. "
Jesus looked at him and loved him. ~Mark 10:19-21a
Jesus said "you know the commandments" to once again confront the man's faith. We may trust the man's assertion that he had faithfully obeyed the commandments. We can be sure that Jesus knew whether it was true. We might suppose that Jesus loved the man because he truly had been obedient to the commandments, but we may also suppose that Jesus loved him because he knew the man could not have kept the commandments though he sincerely desired it. However, by asking Jesus, "what must I do", he has testified that the commandments he has kept are insufficient for salvation. In fact, in Matthew's and Luke's account, the man asks, "what do I still lack?"
The man knows something, if not everything, about Jesus identity. He comes to our Lord the same way I often have. That is, either to establish in front of witnesses that God has already approved of him or to find out what steps must yet be taken. Having no idea how to obtain Jesus public approval, I have said, "I just want to know what I must do -- what prayers I must say, what tasks I must perform, etc. -- to secure my eternal future, so that I can get that taken care of and then get on with my life."
"One thing you lack," he said. "Go, sell everything you have and give to the poor, and you will have treasure in heaven. Then come, follow me. "
At this the man's face fell. He went away sad, because he had great wealth." ~Mark 10:21b-22
I've heard it said that the man lacked willingness to give away his wealth. He was miserly or greedy or both. This is true, but the "one thing" he lacked was not to "sell everything" or to "give to the poor". It was "come follow me", a relationship with Jesus. With all of his obedience to the commandments, the man was still in need of faith in Jesus in order to have eternal life. Even though Jesus encouraged the man, saying he would have eternal treasure, his wealth was an idol for him and stood as an obstacle.
I say in essence, "Just tell me what hoops to jump through, so I can turn my back on you." Jesus says, "Come follow me."