“Dear Friends,

You are now about to go back home. Your friends will want to know how you have changed after being in this lovely city with the Pope and with hundreds of thousands of other young people from around the world. What are you going to tell them? I invite you to give a bold witness of Christian living to them. In this way you will give birth to new Christians and will help the Church grow strongly in the hearts of many others.

During these days, how often I have thought of the young people at home who are waiting for your return! Take my affectionate greetings to them, to those less fortunate, to your families and to the Christian communities that you come from.

… before we say good-bye, and while the young people of Spain pass on the World Youth Day cross to the young people of Brazil, as Successor of Peter I entrust all of you present with this task: make the knowledge and love of Jesus Christ known to the whole world! He wants you to be the apostles of the twenty-first century and the messengers of his joy. Do not let him down! Thank you very much.”

— Pope Benedict XVI, addressing the youth attending WYD, Madrid, 21 August 2011

Full text: http://www.zenit.org/article-33253?l=english