Pope Francis announced that there will be some changes in the Catholic Church this Holy Year in a document presented during a ceremony in front of the Holy Door at St Peter's Basilica on Sunday.

Mercy was a central tenet of the papal bull—the letter Francis distributes to cardinals outlining his plan for the Holy Year, or Year of Jubilee.

"It is time to return to the basics and to bear the weaknesses and struggles of our brothers and sisters," Francis wrote in the papal bull titled, "Face of Mercy."

"The Church, in this time of great historical change, is called to offer more evident signs of God's presence and closeness," he said in a homily following the ceremony.

The Holy Year occurs every 25 years unless the Pope deems it necessary to have one sooner. The next Holy Year was scheduled for 2025.

Francis announced the jubilee year last month, on the second anniversary of his election. It will begin on December 8 — a date that Francis said is "of great significance, for it impels the Church to continue the work begun at Vatican II."

December 8 is also the date of the Feast of the Immaculate Conception, and the date when the Second Vatican Council closed in 1965. The jubilee year will end on November 20, 2016.

During the Holy Year, the Holy Door in St Peter's Basilica will be opened so pilgrims can pass through. Holy Doors in churches around the world will also be opened to symbolise a "sign of communion for the whole Church," the papal bull read.

Francis wrote that those who pass through the doors "will experience the love of God who consoles, pardons, and instills hope."