Thanking cardinals as he looked forward to his inauguration Mass today, he said he was only too aware of the intense burden thrust upon him as spiritual leader of the world’s 1.1 billion Roman Catholics.
"I know well the nature of this mission that I was assigned," he said. "It is not about honors, but about service."
The 78-year-old pope, who was applauded when he entered the Clementine Hall in the Apostolic Palace, asked the prelates for their continuing support.
"Please never let me be deprived of your support," he urged.
Each cardinal then went up to the Pope in turn, knelt, and kissed his hand before exchanging a few words, in images carried by Vatican television.
Earlier Friday, denouncing a draft law by Spain’s lower house of parliament allowing homosexuals to marry and adopt children, the cardinal who heads the Pontifical Council on the Family said it was the duty of Christians to oppose "iniquitous" laws.
"A law as profoundly iniquitous as this one is not an obligation, it cannot be an obligation," Cardinal Alfonso Lopez Trujillo told Italy’s Corriere della Sera newspaper.
Spain is a traditionally Catholic country, and King Juan Carlos and Queen Sofia are due to attend Pope Benedict’s inauguration.
The new Pope is a conservative figure who has taken a strong line in the past on gays, calling homosexual orientation a tendency toward "intrinsic moral evil."
His handling of the latest controversy will be scrutinized for clues as to how he intends to drive forward his papacy in a Church also divided over other hot-button issues such as contraception, abortion, divorce and the ordination of women.
Trujillo said any official asked to conduct a gay marriage should exercise the same conscientious objection as doctors asked to perform an abortion.
"This is not a matter of choice: all Christians... must be prepared to pay the highest price, including the loss of a job," he said.
Madrid rejected the charges. Maria Teresa Fernandez de la Vega, number two in the Spanish government, told a press conference that state officials "must apply the laws that government proposes and parliament approves."
"Every citizen can build a family in line with canon (Church) law if they wish, or civil law if they wish," she said.
The new Pope, who was elected Tuesday by his 114 cardinal colleagues, will be inaugurated at a 10 a.m. (0800 GMT) Mass Sunday that is expected to draw half a million people and a clutch of world leaders.
They will include a strong delegation out of his native Germany, including Chancellor Gerhard Schroeder and President Horst Koehler as well as thousands of ordinary Germans now beginning to flock into Rome.
Among religious dignitaries attending will be the Archbishop of Canterbury Rowan Williams, spiritual head of the 77-million-strong Anglican Communion, as well as leaders of the eastern Orthodox Churches.
At the Mass he will formally receive the insignia of his office, a pallium – a circular band of fabric with a pendant and decorated with square crosses – and the Fisherman’s Ring with the image of Saint Peter, a disciple of Jesus and the first pope in the Church’s 2,000-year history.
"Rome is calmly preparing itself for another extraordinary event," Mayor Walter Veltroni said, after the millions who poured into Rome to mourn John Paul II and attend his April 8 funeral.
Guido Bertolaso, the commissioner in charge of civil security arrangements, predicted at least 100,000 people from Germany would come.
The airspace over Rome will be closed to traffic on Sunday from 8 a.m. to 4 p.m. and Ciampino airport, Rome’s second largest, closed from 1 p.m. on Saturday until 4 p.m. on Sunday.
Meanwhile the Sistine Chapel, where the cardinals elected the Pope under Michelangelo’s magnificent "Last Judgment," will reopen to tourists Saturday after two weeks off-limits, the Vatican museum said.