What is the meaning of Matthew 19:18-20?

18 He saith unto him, Which? Jesus said, Thou shalt do no murder, Thou shalt not commit adultery, Thou shalt not steal, Thou shalt not bear false witness, 19 Honour thy father and thy mother: and, Thou shalt love thy neighbour as thyself. 20 The young man saith unto him, All these things have I kept from my youth up: what lack I yet? (Matthew 19:18-20 KJV)

William Burkitt’s Commentary

Observe here, That the duties which our Saviour instances in, are the duties of the second table, which hypocrites are most failing in; but the sincere practice of our duty to our neighbour, is a singular evidence of our love to God. These duties of the second table the young man says he had kept from his youth, and perhaps might say it truly, according to the Pharisees interpretation, which condemned only the gross, outward act, not the inward lust and motion of the heart.

Learn hence, How apt men are to think well of themselves, and have too high an opinion of their own goodness and righteousness before God: All these have I kept from my youth.