In an unusually public outpouring for such a private man, he alluded to some of the most difficult times of his papacy, which was dogged by sex abuse scandals, leaks of his private papers and reports of infighting among his closest aides.
"Thank you, I am very moved," Benedict told a cheering crowd of more than 150,000 people in St Peter's Square a day before he becomes the first pope to step down in some six centuries.
He said he had great trust in the Church's future, that his abdication was for the good of the Church and asked for prayers for cardinals choosing his successor at a time of crisis.
The Vatican said the address, repeatedly interrupted by applause and cries of "Benedict, Benedict" - was the last by the pope, who as of Thursday evening will have the title "pope emeritus."
"There were moments of joy and light but also moments that were not easy ... there were moments, as there were throughout the history of the Church, when the seas were rough and the wind blew against us and it seemed that the Lord was sleeping," he said.
When he finished the crowd, which spilled over into surrounding streets and included many of the red-hatted cardinals who will elect his successor in a closed doors conclave next month, stood to applaud.
"I took this step in the full knowledge of its gravity and rarity but with a profound serenity of spirit," he said, as people in the crowd wave supportive banners and national flags.
Loving the Church meant, "having the courage to take difficult and anguished choices, always having in mind the good of the church and not oneself," he said.
The pope says he is too old and weak to continue leading a Church beset by crises over child abuse by priests and a leak of confidential Vatican documents showing corruption and rivalry among Vatican officials.
He said he was not "coming down from the cross" but would serve the Church through prayer.
Some of those who have faulted Benedict for resigning have pointed to the late Pope John Paul, who said he would "not come down from the cross" despite his bad health because he believed his suffering could inspire others.
Many Catholics and even some close papal aides were stunned by his decision on Feb. 11 and concerned about the impact it will have on a Church torn by divisions.
Most in the square were supportive of Benedict, an increasingly frail figure in the last months of his papacy.
"He did what he had to do in his conscience before God," said Sister Carmel, from a city north of Rome, who came to the capital with her fellow nuns and members of her parish.
"This is a day in which we are called to trust in the Lord, a day of hope," she said.
"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."
Not everyone agreed.
"He was a disaster. It's good for everyone that he resigned," said Peter McNamara, 61, an Australian of Irish descent who said he had come to the square "to witness history".
The pope, a theologian and professor, never felt truly comfortable with the weight of the papacy and many Catholics feel that, although he was a towering Church figure, perhaps the cardinals should have chosen someone else in 2005.
"It was clear from the start that he was more at home in a library," said Carla Manton, 65.
"A very good man but he realised in his heart that this was the right thing to do for himself and the Church and now he will pray, he will pray for all of us."
Benedict will move to the papal summer residence south of Rome on Thursday night and later to a convent in the Vatican.
He will lay aside the red "shoes of the fisherman" that have been part of his papal attire and wear brown loafers given to him by shoemakers during a trip to Leon, Mexico last year.
He will wear a "simple white cassock", the Vatican said.
His lead seal and his ring of office, known as the "ring of the fisherman", will be destroyed according to Church rules, just as if he had died.
The Vatican said on Tuesday that the pope was sifting through documents to see which will remain in the Vatican and go into the archives of his papacy and which "are of a personal nature and he will take to his new residence".
Among the documents left for the next pope will be a confidential report by three cardinals into the "Vatileaks" affair last year when Benedict's former butler revealed private papers showing corruption and in-fighting inside the Vatican.
The new pope will inherit a Church marked by Vatileaks and child abuse scandals involving priests in Europe and the United States, both of which may have weighed on Benedict's decision.
On Thursday, he will greet cardinals in Rome. That afternoon he will fly by helicopter to the papal summer retreat at Castel Gandolfo, a 15-minute journey.
In his last appearance as pope, he will greet residents and well-wishers in a small square.
At 8pm the Swiss Guards who stand as sentries at the residence will march off in a sign that the papacy is vacant.
Benedict changed Church rules so that cardinals who start pre-conclave meetings on Friday could begin the conclave earlier than the 15 days after the papacy becomes vacant prescribed by the previous law.
The Vatican appears to be aiming to have a new pope elected by mid-March and installed before Palm Sunday on March 24 so he can preside at Holy Week services leading to Easter.
Cardinals have begun informal consultations by phone and email in the past two weeks since Benedict said he was quitting.