Pope Francis on Saturday proclaimed a special year of worldwide efforts by the Catholic Church to stress mercy, not severity, saying the institution's credibility was at stake.

At St. Peter's Basilica Saturday evening, the pope listened as a Vatican prelate read from a papal bull, or decree, in which Francis proclaimed an "Extraordinary Jubilee of Mercy" Holy Year. The year begins Dec. 8 with Francis' opening the normally closed Holy Door in the back of the basilica and ends Nov. 20, 2016.

"The church's very credibility is seen in how she shows merciful and compassionate love," Francis declared in the 12-page long decree.

"In a word, wherever there are Christians, everyone should find an oasis of mercy," Francis said.

Whether this emphasis on mercy will affect church teaching will likely be closely watched by those feeling excluded by the Vatican, including divorced Catholics who remarry and who want Francis to allow them to receive Communion. Gay faithful are also watching to see how they are welcomed.

Francis said the Vatican's modernizing reforms of the 1960s reflected "the need to talk about God ...in a more accessible way" and tear down "walls which too long had made the Church a kind of fortress," he said. Quoting St. John XXIII, who began the reforms, Francis said the church needed to renounce "arms of severity" for the "medicine of mercy."

In explaining his choice of year of mercy, Francis said that "great historical change" means faithful must renew their "capacity to see what is essential" in the church's mission.

In a new practice, Francis announced that in cathedrals and some shrines worldwide, a special "door of mercy" will stay open during Holy Year. 2000 was the last Holy Year.