It was announced last week that the Catholic Church would canonize an Aztec peasant who saw visions of the Virgin Mary near Mexico City in 1531. The decision is not startling in itself -- Juan Diego's miraculous accounts have long been known and credited among believers -- but it is likely to have a wider, symbolic meaning for American Catholics. Their church is changing, and Mexico's "Brown Virgin," Our Lady of Guadalupe, is likely to play a bigger part in it.

Why? The short answer is: Mexican immigration. Though Mexicans have been a part of American Catholicism since the Southwest became U.S. territory in the mid-19th century, only now do their numbers ensure that they will affect the broader faith. "Twenty-first-century American Catholicism will be heavily influenced by Mexican tradition," says Luis Leon, a professor of religious studies at Arizona State University, "not unlike the way the Irish did a century ago."

In recent years the greatest rise in the number of U.S. Catholics has occurred in the six states where the Latino population has grown the fastest. Today roughly a third of American Catholics are Hispanic, most of them Mexican. In Los Angeles, now the largest archdiocese in the nation, two of every three Catholics is Latino.

Earlier waves of immigrants brought with them their own devotional icons. Italians celebrated the feasts of Our Lady of Mount Carmel and Our Lady of Pompeii. The Irish honored Saint Patrick, while German Catholics preferred St. Boniface and Poles venerated St. Stansilaus. But the assimilation and mobility of white ethnic Catholics -- combined with a movement to refocus attention on the rites and rituals of the church -- led to a decline in devotional Catholicism after the 1950s, when American Catholics were overwhelmingly native-born, middle-class and white.

That decline is likely to reverse as Mexican immigrants -- the largest Catholic immigrant group in U.S. history -- bring their own brand of devotion here. But the Mexicanizing of American Catholicism is not limited to a renewed veneration of the Virgin. "Mexicans like more color in churches," says the Rev. Virgilio Elizondo, a theologian and the former rector of San Fernando Cathedral in San Antonio, Texas. "We like statues, banners and music. We love to include all our senses. Our worshipping is very celebratory."

And such celebration often takes place outside the church, in pilgrimages and front-yard altars. It would be hard to find a Southern California grocery without devotional candles. Mexicans have brought us the tradition of creating sidewalk shrines where people have died. The Virgin is painted on walls in Mexican neighborhoods. "We bring our religion into the public space," Father Elizondo says.

Mexican religious observance also concentrates more on cultural practice than orthodoxy. "Mexicans don't have the same institutional attachment to the church as have some other immigrant groups," says Mary Gautier of the Center for Applied Research in the Apostolate in Washington. "Their Catholicism is not as tied to parish registration or sending their children to Catholic schools."

Some theologians believe that the influence of Mexicans on American Catholicism may tone down the polemics within the church. "Mexican Catholicism is not concerned as much with dogma," says the Rev. Allan Figueroa Deck, director of the Loyola Center for Spirituality in Orange, Calif. "The values of Hispanic culture tend to be communicated not by precise doctrine but through symbols."

But even as Mexicans are wielding greater influence on the American church, America is changing them, too. For instance, only a small percentage of Catholics south of the border attend Mass every Sunday, in part because Mexico has long suffered from a shortage of priests. But Mexican immigrants begin to attend church more regularly as they acculturate into U.S. life. And latter-generation Mexican-Americans sometimes slip away from Catholicism into Protestant faiths. While only 18% of foreign-born Latinos call themselves Protestant, 32% of third-generation Latinos do.

Still, that doesn't always mean losing their devotion to the patroness of Mexico. Lydia Lopez, the first Mexican-American to be named a canon in the Episcopal Church of Los Angeles, has integrated Juan Diego's visions into her religious life. "I am a great fan of the Virgin of Guadalupe," she says. "She is a very important spiritual and cultural symbol who is not just for Catholics but for all of us."