Pope questions abuse by priests

The weeklong Eucharistic Congress, held by the Vatican every four years in a different part of the world, took place against a backdrop of deep anger over child abuse cover-ups and surveys showing declining weekly Mass attendance in Ireland, where church and state were once tightly entwined.

"How are we to explain the fact that people who regularly received the Lord's body and confessed their sins in the sacrament of Penance have offended in this way?" said the pope, referring to church staff who abused children.

"It remains a mystery," he said. "Yet evidently their Christianity was no longer nourished by joyful encounter with Jesus Christ. It had become merely a matter of habit."

Dublin Archbishop Diarmuid Martin has said the church in Ireland is facing a grave fight for survival.

"Your forbears in the church in Ireland knew how to strive for holiness and constancy in their personal lives," Benedict said.

In a reference to the Vatican's insistence on Sunday Mass attendance, Benedict said Catholic faith ''is a legacy that is surely perfected and nourished" at Mass.