Associated Press

Pope Francis declared today that mercy trumps moralizing in the Catholic Church, as he opened a special Holy Year marked by unprecedented security aimed at thwarting a Paris-style attack at the Vatican.

Francis celebrated a special Mass in a rain-soaked St. Peter's Square to formally open his "revolution of tenderness." The celebration was capped with the opening of the basilica's big bronze Holy Door through which upward of 10 million pilgrims will pass over the course of the year.

Pope opens Holy Door Pope Francis opens the Holy Door at St. Peter's Basilica, inaugurating the Holy Year of Mercy on the feast of the Immaculate Conception. Posted by Catholic News Service on Tuesday, December 8, 2015

Some 5,000 extra police, carabinieri and soldiers were deployed around Rome, and a no-fly zone imposed on its skies, to protect the pilgrims who are flocking to Rome on foot, by car, train and plane to participate.

Francis launched the 12-month jubilee to emphasize what has become the leitmotif of his papacy: showing the merciful and welcoming side of a Catholic Church more often known for its moralizing and judgment.

"How much wrong we do to God and his grace when we speak of sins being punished by his judgment before we speak of their being forgiven by his mercy," Francis said in his homily in front of a crowd of an estimated 50,000. "We have to put mercy before judgment, and in any event God's judgment will always be in the light of his mercy."

At the end of the Mass, Francis pushed open the basilica's Holy Door and walk through it to symbolize the pilgrimage of life's journey and the sacrifices that must be endured to find God's mercy. Emeritus Pope Benedict XVI attended.

Tonight, the Vatican will lend itself to another one of Francis' preoccupations — environmental protection. A coalition of humanitarian groups has banded together to screen images of nature by well-known photographers and filmmakers on the facade of St. Peter's.

Security was tight, with police and civil protection crews checking bags and passing metal-detecting wands over each of the tens of thousands of people attending the Mass.

"We have to absorb the message that God always forgives us, which is the message that the pope gives to us," said Maria Sila, a pilgrim from Buenos Aires as she waited for the Mass to begin.

Holy Years are generally celebrated every 25-50 years, and over the centuries they have been used to encourage the faithful to make pilgrimages to Rome to obtain an "indulgence" — the ancient church tradition related to the forgiveness of sins that roughly amounts to a "get out of Purgatory free" card.

Unlike in Martin Luther's time, these Holy Year indulgences are free and available to those who pass through the Holy Door.

The last jubilee was in 2000, when St. John Paul II ushered in the church's third millennium and some 25 million pilgrims flocked to a Rome that had undergone a multimillion-dollar facelift for the occasion.

In typical Francis fashion, the pope made clear from the start that he wanted this Holy Year to be a more sober occasion. For the first time, the pope instructed all cathedrals around the world to open their Holy Doors to pilgrims to encourage the faithful to mark the jubilee at home rather than coming to Rome.

Nevertheless, Italian officials seized on the excuse of the jubilee to allocate millions of euros for dozens of public works projects around the capital, practically none of which has been completed.

The Vatican's lead organizer for the jubilee, Archbishop Renato Fisichella, lamented last week that the Vatican had essentially wasted four months of planning time thanks to a local political scandal that resulted in Rome's mayor being ousted midway through the jubilee preparations. Fisichella said all the Vatican wanted were refurbished sidewalks leading to St. Peter's to make sure pilgrims don't trip on potholes or crooked cobblestones. Several of those streets remain closed as construction work continues.

Francis announced his Holy Year on the second anniversary of his papacy, saying his aim was "to give comfort to every man and every woman of our time." It was in keeping with his priority to make the church a "field hospital" for injured souls, where the wounded are welcomed and loved, not judged.

The jubilee year will feature a host of special Masses and extra general audiences to accommodate the throngs of pilgrims, while Francis himself has set aside one Friday each month to slip out of the Vatican to perform an act of mercy himself, in private.

For all the pomp of Tuesday's ceremony, Francis technically launched the Holy Year of Mercy last week in Central African Republic, when he pushed open the Holy Door of the Bangui cathedral. His aim was to give the conflict-weary Christians there a spiritual boost, and show the universality of his message of mercy.

Elsewhere around the world, Holy Doors will be opening at cathedrals starting this Sunday.