Pope Francis has celebrated his first Mass since becoming the Catholic Church's head, giving a homily in front of cardinals in the Sistine Chapel.
"I would like all of us... to have the courage to walk in the presence of God," he said, speaking in Italian.
Earlier, the pontiff said private prayers at the basilica of Santa Maria Maggiore, after which he met children and commuters heading to work.
He was also starting the process of appointing senior staff at the Vatican.
As the first Latin American - and the first Jesuit - pope, Francis has received a flood of goodwill messages from around the world.
But the 76-year-old Argentine, formerly Cardinal Jorge Mario Bergoglio, also faces a series of tough challenges.
The Church has been dogged by infighting and scandals over clerical sex abuse and alleged corruption.
The BBC's David Willey, in Rome, says that Pope Francis becomes head of the Church at a critical moment in its history.
Shunned special car
On Wednesday night, Pope Francis endeared himself to the crowds in St Peter's Square - and underlined his reputation for humility - when he asked them to bless him before blessing them in return from the balcony of the basilica.
The Vatican's account of his first hours in the top job also emphasised Pope Francis's humility, describing how he shunned a special car and security detail provided to take him to the Vatican and travelled on a bus with the other cardinals.
Following his first outing as pope to the Rome basilica on Thursday, Francis went back to the clergy house in a city centre side street where he had been staying ahead of the conclave that elected him on Wednesday.
"He packed his bags and then he went to pay the bill for his room so as to set a good example," said Vatican spokesman Federico Lombardi.
He also broke tradition by remaining standing to receive cardinals' acts of homage after his election, instead of sitting in the papal throne, Lombardi said.
On Friday, he will meet all the cardinals, including those aged over 80 who did not take part in the conclave.
On Saturday he will meet the world's media at a special papal audience, an opportunity perhaps to set out some of his global vision, says the BBC's James Robbins in Rome.
A visit to his predecessor Benedict XVI at his retreat at Castel Gandolfo outside Rome is also planned, but will not take place in the next couple of days, Lombardi said.
The visit to Benedict is important, correspondents say, as the existence of a living retired pope has prompted fears of a possible rival power.
Francis will be installed officially in an inauguration Mass on Tuesday 19 March, the Vatican added.
Force of reform?
The election of Cardinal Jorge Mario Bergoglio surprised many observers when it was revealed on Wednesday.
Although he reportedly came second to Pope Benedict XVI during the 2005 conclave, few had predicted the election of the first pope from outside Europe in 1,300 years.
Pope Francis is regarded as a doctrinal conservative, but he is also seen as a potential force for reform of the Vatican bureaucracy - and analysts say that may have won the support of reforming cardinals.
The new pontiff will certainly come under strong pressure to reform the Curia, the governing body of the Church.
He will also face an array of challenges which include the role of women, interfaith tensions and dwindling congregations in some parts of the world.
The 76-year-old from Buenos Aires is the first Pope to take the name of Francis - reminiscent of Francis of Assisi, the 13th Century Italian reformer and patron saint of animals, who lived in poverty.