Cardinal Joseph Ratzinger has told fellow prelates today they must choose a new pontiff who would defend traditional teachings and reject attempts to modernise doctrine.
Cardinal Ratzinger, a 78-year-old German who is seen as a front-runner to become pope, issued his stern warning to other cardinals at a Mass just hours before they were to be locked up in a conclave to find a successor to Pope John Paul.
Cardinal Ratzinger
All of the 115 cardinal electors under the age of 80 who will enter the conclave joined older cardinals, bishops, priests, nuns and the simple faithful in today's service in St. Peter's Basilica.
The faith of many Christians had been shaken "by so many currents, ideologies and different ways of thinking" and the Catholic Church faced an uncertain future threatened by the rise of Christian sects around the world, Cardinal Ratzinger, the Vatican's doctrinal chief, said in a homily.
"Having a clear faith according to the creed of the Church is often labelled as fundamentalism," he said, adding that the Church had to reject "a dictatorship of relativism" that denied the existence of absolute truths.
"An adult faith is not one that follows tides of trends and the latest novelties. To be adult and mature the faith must be deeply rooted in friendship with Christ," he said.
Since John Paul's death on April 2th, media and bookmakers have tipped Cardinal Ratzinger as the early favourite to succeed him.
But most Vatican experts doubt that the German, whose conservative dogma has polarised the Catholic world, will be able to secure the two-thirds majority needed to become pope, leaving the field wide open.
In papal conclaves, it is considered a disadvantage to break from the pack too early.
The conclave, a unique election mixing ancient ritual with ultra-modern technology, was due to start in the frescoed Sistine Chapel at about 2.30 Irish time.