What is humility?
Humility is accepting the truth of yourself, not putting yourself down. So for example, let us pretend that you are a world renowned pastry chef, and that the Pope has asked you to prepare a dessert for a banquet he is having with the President of the United States at the Vatican. The Pope tells you that he has had your pastries many years ago at your shop in Washington, DC, when he was a cardinal visiting America. The Pope tells you that he fell in love with your apple strudel, and asks you if you could provide your apple strudel for his banquet, and tells you that God has gifted you with a talent he has not seen in his entire life.
For the scenario I have presented, what would be the humble response? As I mentioned, humility is accepting the truth of yourself, so the response would go something like this: “Thank you Holy Father for the complement. I am so grateful for everything Christ has given me. It would be a great honor to cook for you.”
So when Jesus tells us to be humble in Luke 18: 9 -14, Christ is not telling us to put ourselves down, but to accept the truth of ourselves (i.e., the blessings Christ has given us). To understand more about the importance of humility, read the Catholic Encyclopedia's article: Humility.