Luke 10:29 KJV
But he, willing to justify himself, said unto Jesus, And who is my neighbour?
Came to the right man
Jesus Christ is the only one qualified to answer the question which is the great commandment. Man's opinions on this matter hold no weight. Only God is qualified to answer the question.
Asked the right questions
A man needs to know what the expectations of the Lord are. True enough; the law was not given that a man would obtain righteousness through its keeping. God had another thing in mind. To find out the mind of God; this was wise indeed.
But he gave the completely wrong response
Coming under conviction he should have appealed to the Lord's mercy and found that God Himself was willing to justify him. Instead he did what is the natural and satanic thing, he wanted to justify himself. He did not want to confess his guilt and seek justification from God. He wanted to maintain his own god like status. God was willing to justify him through Jesus Christ. But he would rather justify himself.
This is our trouble too. When confronted with our sin rather than humbling ourselves and confessing it, we seek to justify and excuse it.