"In this image taken from video as Pope Benedict XVI enters to deliver his final greetings to the assembly of cardinals at the Vatican Thursday Feb. 28, 2013, before he retires in just a few hours.  Benedict urged the cardinals to work in unity and promised his ""unconditional reverence and obedience"" to his successor in his final words to his cardinals Thursday in a poignant and powerful farewell before he becomes the first pope in 600 years to resign. (AP Photo/Vatican TV)"