By Ben Brumfield and Ben Wedeman, CNN

Vatican City (CNN) – Pope Benedict XVI delivered his final public prayer ceremony Sunday to a crowd of thousands at St. Peter's Square in Vatican City.

And he explained his decision to step down.

"Thank you for your affection," the pope told the crowd as he appeared at the window of his apartment overlooking the square.

As is customary, he opened the weekly Angelus prayer with a short sermon.

Benedict spoke on the Transfiguration of Christ, one of the key moments in Jesus' life on Earth, when, according to the church, he took three disciples to pray on a mountain. During his prayers, Jesus was miraculously changed and filled with light.

The crowd interrupted Benedict with rousing applause, as he told them that God wanted him to do the same.

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