VATICAN CITY (RNS) Fifty years after the Second Vatican Council revolutionized life inside the Roman Catholic Church, hundreds of bishops from around the world are gathered in Rome to confront an external threat: a mounting tide of secularization.

The Synod of Bishops on “New Evangelization” brings together 262 top church leaders for a three-week summit at the Vatican, joined by lay experts and representatives of other Christian groups.

In a wide-ranging speech aimed at setting the tone for the bishops' discussion, Washington Cardinal Donald Wuerl called on Christians to “overcome the syndrome of embarrassment” about their faith with a more assertive offense against the “tsunami of secular influence” that is sweeping away “marriage, family, the concept of the common good and objective right and wrong.”

Wuerl has been appointed by Pope Benedict XVI as the “relator general” of the synod, with the key task of summing up the main points of the bishops' discussions.

The synod is timed to coincide with the anniversary of the opening of the Second Vatican Council (1962-1965), which not only transformed the laity and liturgy of the church, but also reoriented the church's engagement with the modern world.

Benedict, who attended Vatican II as a young theologian, has called for a “Year of Faith” to mark the anniversary. He will celebrate a solemn Mass with the few surviving council fathers on Thursday (Oct. 11).

While the council marked a moment of renewal and enthusiasm for the church, Wuerl said it was followed by decades of poor teaching and substandard worship -- “aberrational liturgical practice,” he called it -- that made “entire generations” of Catholics incapable of transmitting the faith to their children and to society at large, ushering in today's secularized society.

Symptoms of this trend are a decline of faith and a shrinking number of Catholics in the Western world but also in traditional Catholic strongholds such as Latin America. Church marriages are decreasing, too, while divorce is all but mainstream.

Catholic leaders in the U.S. and Europe are also worried about a perceived rise of “aggressive” secularism, which they say wants to curtail the church's role in the public sphere and reduce faith to a private exercise.

But in an off-the-cuff meditation in front of the gathered bishops on Monday morning, Benedict was careful to frame the debate as a positive proposal of the church's timeless doctrine to contemporary society.

“Our role in the new evangelization is to cooperate with God,” he said. “We can only let people know what God has done.”

“New evangelization means announcing the faith to those regions that have been Christian for centuries but are now swept by the winds of secularism and religious indifference,” said professor Ilaria Morali of the Pontifical Gregorian University in Rome.

She stressed that while it is important for the church to harness modern technology to “spread the good news,” the essential part of new evangelization is “revitalizing” the church itself, letting Christians rediscover the “joy” and the “responsibility” that comes from faith.