Roman Catholics throughout the English-speaking world on Sunday left behind words they have prayed for nearly four decades, flipping through unfamiliar pew cards and pronouncing new phrases as the church urged tens of millions of worshipers to embrace a new translation of the Mass that more faithfully tracks the original Latin.

The introduction of the new English translation of the Roman Missal, the book of texts and prayers used in the Mass, appeared to pass smoothly in churches, despite some confusion and hesitancy over the new words.

But behind the scenes, the debate over the new translation has been angry and bitter, exposing rifts between a Vatican-led church hierarchy that has promoted the new translation as more reverential and accurate, and critics, among them hundreds of priests, who fear it is a retreat from the commitment of the Second Vatican Council in the 1960s to allowing people to pray in a simple, clear vernacular as they participate in the church’s sacred rites.

There was no reference to that history Sunday morning in the cavernous nave of St. Patrick’s Cathedral, on Fifth Avenue in Manhattan, where Msgr. Robert T. Ritchie, in purple robes to mark the start of Advent, told thousands of worshipers, “Today is a special day — today is the start of a new translation of the Mass,” and directed them to follow the new words listed on laminated pew cards.