Vatican City, USA - Pope Benedict XVI opened a three-week meeting of over 250 Roman Catholic bishops at the Vatican, telling the synod it was "hypocritical" to exclude religion from public life.
The 78-year-old pontiff's first synod since his April 19 election will tackle the problems facing the Roman Catholic Church at the beginning of his pontificate and will focus largely on theological issues linked to the Eucharist, the Christian service of Holy Communion.
But more importantly for the wider world, it will also touch on thorny social problems like abortion and divorce, as well as attendance at Sunday mass and ecumenism.
"A tolerance which allows God as a private opinion but which excludes Him from public life, from the reality of the world and our lives, is not tolerance but hypocrisy," the pope said in the homily he gave at the synod's opening mass in St Peter's Basilica.
"When man makes himself the only master of the world and master of himself, justice cannot exist," the pontiff added. "Then, arbitrariness, power and interests rule."
The synod, which brings together 252 bishops from 118 countries, opened at 9:00 am (0700 GMT) without the participation of four Chinese bishops whom Benedict XVI had asked to take part.
The bishops -- three from China's state-controlled church, which is not recognised by the Vatican, and one from the underground Catholic church, which is persecuted by Beijing -- were not authorised by Beijing to attend the meeting.
At this 11th synod meeting, which will run until October 23, bishops will debate how to address falling church attendance in Europe, America and Oceania, where the number of faithful attending Sunday mass has dropped well below that of Africa and Asia.
They will also remind Catholics of their duties regarding receiving Holy Communion at mass, and that people who support "immoral choices in life, such as abortion," cannot participate in the Eucharist.
Means of strenghtening the unity of the church -- a stated aim of Benedict XVI's -- will also be debated, despite differing conceptions of the Eucharist among the world's Churches.
Catholics believe wafers of unleavened bread and wine are transformed into the body and blood of Jesus Christ during the ceremony.
On the last day of the synod, Benedict XVI is expected to announce the names of five new saints, continuing the process of regularly conferring sainthoods which was started by his predecessor, John Paul II.
A working document published by the Holy See in September, based on the views of 4,500 bishops worldwide, highlighted specific social problems facing the Church.
"Some receive communion while denying the teachings of the Church or publicly supporting immoral choices in life, such as abortion, without thinking that they are committing an act of grave personal dishonesty and causing scandal," it said.
The bishops' gatherings were begun by Pope Paul VI in 1965, though a number of extraordinary synods have been convened to discuss the Church's difficulties in Africa, America, Lebanon, Europe and Oceania.