St. Louis ? At least 1,500 people attended Christmas Eve Mass presided by an excommunicated Roman Catholic priest, despite warnings from the archbishop that participating would be a mortal sin.

The Rev. Marek Bozek left his previous parish without his bishop’s permission and was hired by St. Stanislaus Kostka Church earlier this month. As a result, Bozek and the six-member lay board were excommunicated last week by Archbishop Raymond Burke for committing an act of schism.

Burke said it would be a mortal sin for anyone to participate in a Mass celebrated by a priest who was excommunicated – the Catholic Church’s most severe penalty. Burke, who couldn’t stop the Mass, said it would be “valid” but “illicit.”

Despite the warning, Catholics and non-Catholics filled the church. An overflow crowd viewed the Mass by in an adjoining parish center.

“I’m not worried about mortal sin,” said worshipper Matt Morrison, 50. “I’ll take a stand for what I believe is right.”

Many wore buttons reading “Save St. Stanislaus,” and said they wanted to offer solidarity to a wronged parish.

When Bozek entered, the congregation rose and greeted him with thunderous applause.

Bozek, a Pole who arrived in the U.S. five years ago, said he agonized about leaving his previous parish but wanted to help a church that had been deprived of the sacraments for 17 months.

To be Polish is to be Catholic, he said, and to be Catholic is to receive the sacraments.

Bozek said he doesn’t believe that receiving sacraments at St. Stanislaus, especially Holy Communion, puts a Catholic at risk of mortal sin, in which the soul could suffer eternal damnation.