Pope Benedict XVI assured a huge, cheering crowd at the Vatican Wednesday that he was not abandoning the Catholic Church, saying he would remain at its service through prayer.
"I ask each of you to pray for me," he told tens of thousands who gathered in the sunshine to watch his final general audience before Thursday's abdication.
"There were moments when the waters were choppy and there were headwinds," he said.
He said he was not "coming down from the cross" despite renouncing his office, saying his decision was taken "in full awareness of its gravity and rarity but also with profound serenity of spirit."
Earlier, pilgrims and onlookers from around the world cheered as Benedict arrived and made a circuit of the square on his "popemobile."
Benedict waved as he swept through the crowd, pausing briefly several times to bless babies, before heading to a platform in front of St. Peter’s Basilica to make his address.
Among the audience was New Yorker Elise O'Donnell-Tixon, who is now living in Rome. "I'm sad because this will likely be the last time I see him," she said. "I was lucky, because my husband and I were blessed by the pope at an audience last Christmas. We got front-row seats."
At the end of the speech, the crowd stood to applaud.
Vatican communications adviser Greg Burke told TODAY that Pope Benedict had appeared to be calm during the speech, despite the emotion of the occasion.
"He has always been very serene," Burke said. "Above all else, he showed he has faith. His message was that it's not our church, it's not my church, it's the church of Christ."
Vatican organizers said more than 50,000 had applied for official tickets for Wednesday’s event – eight times the usual number of applications. An estimated total of 200,000 were expected in square and surrounding streets.
The size of the event means there was not expected to be any kissing of the pontiff’s hand as is traditional after papal audiences.
Young members of the Catholic group Opus Dei served as stewards at the entrance to the square, managing the queues of people filing in past metal detectors, AFP correspondent Gildas Le Roux reported.
Not all of them supported Benedict's resignation, Le Roux said, quoting one of the stewards, Leonardo Rossi, as saying: "I do not share the pope's decision to step down. It is not a fitting time, with all the problems the church is going through."
Many in the crowd waved flags and banners wishing the pope well, although the overall tone of the event remained sombre.
Sister Carmela, who lives north of Rome, traveled to the square with her fellow nuns and members of her parish, Reuters said.
"He did what he had to do in his conscience before God," she told Reuters. "This is a day in which we are called to trust in the Lord, a day of hope. There is no room for sadness here today. We have to pray, there are many problems in the Church but we have to trust in the Lord."
Tens of thousands had been in the square since early Wednesday in the hope of securing a good place from which to see the audience.
Among them was a marching band from Pope Benedict’s native Germany. Balthasar Bauer, 23, from Bavaria, who was in traditional dress, lederhosen, said: "This will likely be the last Bavarian pope, so I had to come here to see him for one last time."
After the address, the Pope's Twitter account, @Pontifex, posted a message that said: "If only everyone could experience the joy of being Christian, being loved by God who gave his Son for us!"
Pope Benedict will leave his residence inside the Vatican and travel by helicopter to his summer residence at Castel Gandolfo, about 15 miles south-east of Rome at about 4.55 p.m. local time (10:55 a.m. ET) Thursday. His papacy will officially end at 8 p.m. local time (2 p.m. ET).
After stepping down, the pope will keep his name, His Holiness Benedict XVI, but get a new official title, "Emeritus Pope." The Vatican on Tuesday said he would wear a simple white cassock and swap his traditional red shoes for a pair of brown leather loafers he was given on his trip to Leon in Mexico last year.
Meanwhile, the Vatican said Wednesday that the date of the conclave to elect Benedict's successor may not be known until after Monday.
Father Federico Lombardi told the Catholic News Service that cardinals eligible to take part cannot set a start date for the conclave until they have met at the Vatican, and that invitations for them to meet will not be sent out by Cardinal Angelo Sodano, dean of the College of Cardinals, until Friday.
NBC News' Carlo Angerer and Andy Eckardt and Reuters contributed to this report.