From The Gospel of Mark by Mary Healy, comnenting on Mark 10:18
Jesus’ initial response is puzzling and has occasioned much speculation. Why do you call me good? No one is good but God alone. But the mistake is to assume that Jesus is repudiating the attribute of good for himself. He is not denying that he is good; rather, he is inviting the man to reflect more deeply on what he has just said (see 10:3; 12:35; John 2:4 for similar examples). On what basis does he call Jesus good? Is it because he is a wise teacher and powerful miracle worker? Because he treats everyone with kindness? Or is there a more profound basis for Jesus’ goodness? Does the man recognize that ultimately, God alone is good, and that what he perceives in Jesus is not merely unusual human qualities but that infinite goodness that belongs to God alone? Jesus gently directs the man’s gaze toward the answer to his heart’s longing.