Jesus: "Why do you call me good?"

Mark 10:17 When he was gone forth into the way, there came one running, and kneeled to him, and asked him, Good Master, what shall I do that I may inherit eternal life?

• The Complete Jewish Bibl

  Mark 10:18 (CJB) 

  Yeshua said to him, "Why are you calling me good? No one is good except God!

  
  

  "Only through God's unique light can we see good." Metzudat David 

Commentary
Instead of reading the question and statement by Yehoshua to the rich young man as having something to do with teaching either the rich young man or us about the divine or human nature of Yehoshua, we can read it in the light of the statement by Metzudat David.  From the context we learn that the rich young man was fully observant of the mitzvoth (commandments) of the Torah.  He was confident in himself to be able to recognize a "good" teacher.  

Our very first need and our very last need is to have no confidence in ourselves, but to pray whole-heartedly for the mercy of God to reveal his unique light to us by which alone we can see good.  Had the rich young man left all to follow Yehoshua, through that very act, he would have acquired that humility that can receive the unique light of God to see good, which comes only through the mercy of God.

"RaSHI and Metsudat David explain that "Israel's power" and "the power of the holy people" will be broken. At the same time it refers to Deut. 32:36, where it says that God will have mercy on his servants "when he sees their strength is gone and no one is left." Here are used the words "yir'e ki-azlat yad", that is, "he sees that the hand (that is, power) has ceased." The Hebrew expression "everything is at an end", "efesh, atzur ve-azuv", means literally "nil, stopped and rejected." This means that God has mercy on his servants when they feel that they are quite brought to nil, stopped and rejected. Just then they are acceptable to God."  Risto Santala