Lawyers ask a lot of questions. I guess it's their job and they get good at it. The lawyer who approached Jesus used questions to try to "justify himself," I think what Luke means is that he was trying to figure out how to conform the Scripture to fit his life, rather than conforming his life to fit the Scripture.
Jesus, being a good teacher, answers the lawyer's questions with a question of his own and then a story with a poignant application.
When asked how to inherit eternal life, Jesus asks the lawyer what the Law says. The lawyer gives a good answer: Love God, Love Neighbor. Jesus commends him. Then, the lawyer asks, "Who is my neighbor?"
Was he looking for clarification? Luke says he was trying to justify himself. I really don't think he wanted to hear the answer Jesus gives. I'm not sure I do, either.
Jesus basically says my neighbor is the least likely person I would pick to show my love. The person at the bottom of my list of people worthy of respect and honor, that person is my neighbor. Not the person I like, not the one who looks like me, thinks like me, patronizes the same establishments I do... oh, they're included in "neighbor," but the one I missed, the one I don't want to love, that's my real neighbor. That's who God says to me, love the same way I love myself.
Jesus tells a story and makes the Samaritan, a mixed-breed, heretical race of people, the hero. He's the one who acted like a neighbor. He went out of his way to bless someone who would naturally have hated him.
Then Jesus rubs salt in the wound by saying to the lawyer, "Oh, by the way, you go and do the same thing. It is eternal life your after, right? Then start by bringing some eternity into this life by acting like you belong to the God who created all and loves all."
Ouch. If Jesus doesn't challenge my most dearly held beliefs and ethics, then I'm not sure I have actually encountered the real Jesus, the Jesus of Luke 10:25-37.