VATICAN CITY — Pope Benedict XVI in his New Year’s homily Sunday praised young people as key to securing a future of hope despite what he called “shadows on the horizon of today’s world.”

In the splendor of St. Peter’s Basilica, with ambassadors to the Holy See from dozens of countries seated in the front rows, the pontiff, wearing white vestments with gold-colored trimmings, celebrated Mass on a day the Vatican dedicates to world peace.