Pope Benedict began a three-day pilgrimage at the Catholic shrine of Lourdes in southwestern France after telling a huge crowd in Paris that the modern world had made idols of money and power.
Benedict (81) plans to say two masses and join pilgrims in processions to mark the 150th anniversary of the apparitions of the Virgin Mary to Bernadette Soubirous.
At the shrine sanctuary, about 45,000 faithful waited in the cold rain for an address from Benedict, who visited a church with the font where Bernadette was baptised, and then the small room where she lived at the time of the apparitions in 1858.
The Catholic primate Cardinal Seán Brady is in Lourdes for the anniversary.
At mass this morning in Paris, the pope told more that 250,000 people - including around 1,500 Irish pilgrims from the diocese of Meaht - that the modern world had turned money, possessions and power into idols as false as the gold and silver statues worshipped by the pagans of antiquity.
"Has not our modern world created its own idols?" he asked. "Has it not imitated, perhaps inadvertently, the pagans of antiquity, by diverting man from his true end, from the joy of living eternally with God," he said in fluent French, wearing gold, white and red vestments.
Benedict, who arrived in France yesterday, celebrated the mass at Les Invalides, a complex of military buildings begun by King Louis XIV in the 17th century that houses the sarcophagus of Napoleon Bonaparte.
In his homily, he pursued a theme dear to him: the need to inject lasting spiritual and religious values into a modern society often enamoured of things material and fleeting.
He quoted the writings of St Paul, saying "Money is the root of all evil", and added in his own words: "Have not money, the thirst for possessions, for power and even for knowledge diverted man from his true destiny?"
Since he arrived yesterday, the pope has been encouraging Catholics to speak out confidently in a country where the separation of church and state that often relegates faith to the private sphere, is part of the national psyche.
The once powerful French church struggles with a shortage of priests and Sunday mass attendance is below 10 per cent.
In his battle to re-inject religious values into French and European public life, Benedict has an unlikely ally in French President Nicolas Sarkozy. Mr Sarkozy, who is twice divorced, has broken a political taboo by speaking openly and positively about the role of religion in society.
In a speech yesterday, he said it would be "folly" for France to ignore its long history of Christian thought.