Before a St. Peter's Square crowd estimated at 100,000 people, Pope Benedict XVI celebrated his last public prayer as pontiff.
The pope said he was following God's wishes by stepping down.
Benedict, 85, has said he is resigning for health reasons.
He said "the Lord is calling me to climb the mountain" and added he will dedicate himself to prayer and meditation after stepping down on February 28.
The pope will make his last public appearance as pontiff on February 27.
On February 28, he will hold one last meeting with cardinals and his resignation -- the first papal resignation in nearly 600 years -- will take effect at 8 p.m.
The Vatican has said it hopes a new pope will be selected before the Catholic Church begins celebrating Easter on March 31.
Based on reporting by AFP, Reuters, and dpa