Pope Benedict XVI giving his farewell speech
Pope Benedict XVI has admitted he faced "choppy waters" during his eight years at the helm of the Roman Catholic Church, but says he was guided by God and felt his presence every day.
The Pope, 85, will retire on Thursday - the first pope to abdicate since Gregory XII in 1415.
Thousands of pilgrims gathered in St Peter's Square in the Vatican for Pope Benedict's final general audience.
His successor will be chosen in a conclave to take place in March, reports the BBC.
Pope Benedict told the crowd his papacy had been "a heavy burden" but he accepted it because he was sure that God would guide him.
At times he "felt like St Peter with his apostles on the Lake of Galilee", he said, making reference to the Biblical story when the disciples were battling against heavy waves and Jesus Christ appeared to them.
After Benedict XVI steps down, he will become known as "pope emeritus".
"I took this step [resignation] in full awareness of its gravity and novelty but with profound serenity of spirit," he said in his address.
The surprise announcement of his abdication has required the rules of electing a successor to be changed to allow the next pope to be chosen before Holy Week, which leads up to Easter.
The white "popemobile" rolled slowly through St Peter's Square, carrying the 85-year-old Pontiff, who waved to the assembled pilgrims.
They chanted his name and thanked him for his service to the Church. At one point, Pope Benedict paused to kiss a baby who was passed up to him.
Many of the cardinals who will elect his successor are in the square.
The BBC's Alan Johnston in Rome says that on Thursday the Pope will travel by helicopter to his summer residence at Castel Gandolfo, about 15 miles (24km) south-east of Rome. He will cease to be Pope at 20:00 local time.
He will retain the honorific "His Holiness" after his abdication and will continue to be known by his papal title of Benedict XVI, rather than reverting to Joseph Ratzinger.
He will wear his distinctive white cassock without any cape or trimmings, but will surrender his gold ring of office and his personal seal will be destroyed.
He will also give up wearing his red shoes.