Vatican City: Pope Benedict XVI hailed Christ's humility, urging the faithful to look beyond the Christmas "glitter" and "enlightened reason", and issued a powerful message for peace.

"Today Christmas has become a commercial celebration, whose bright lights hide the mystery of God's humility, which in turn calls us to humility and simplicity," the pope told thousands at mass in Saint Peter's basilica.

"Let us ask the Lord to help us see through the superficial glitter of this season, and to discover behind it the child in the stable in Bethlehem, so as to find true joy and true light," the 84-year-old pontiff said on Saturday.

The German pope also called for a strengthening of faith over liberal reason, drawing an analogy with the small doorway of the Church of the Nativity in Bethlehem intended to defend the church from raiders on horseback.

"It seems to me that a deeper truth is revealed here, which should touch our hearts on this holy night: if we want to find the God who appeared as a child, then we must dismount from the high horse of our 'enlightened' reason.

"We must set aside our false certainties, our intellectual pride, which prevent us from recognising God's closeness," he said.

He also issued a scathing rebuke against "oppressors" and warmongers around the world saying Christ would be victorious over them.

"At this hour when the world is continually threatened by violence in so many places and in so many different ways, when over and over again there are oppressors' rods and bloodstained cloaks, we cry out to the Lord," he said.

"In this time of ours, in this world of ours, cause the oppressors' rods, the cloaks rolled in blood and the footgear of battle to be burned, so that your peace may triumph in this world of ours," he added.

The pope also voiced a special prayer for those "in poverty, in suffering, as migrants".

The Catholic Church has also this year again been rocked by revelations about sexual abuse by priests and cover-ups by bishops stretching back decades including in Ireland, the Netherlands and the US.

The Vatican has urged all bishops' conferences around the world to come up with guidelines on how to deal with abuses by spring of next year.