ROME — No papal document in recent decades has generated as much pre-release interest as Laudato Si, an encyclical letter written by Pope Francis that the Vatican will release Thursday.

Considering the author’s global popularity, the high profile created by his office, and the politically polarizing topic – the environment, especially his insistence on action on climate change – the buzz is not surprising.

Also feeding interest is the fact that an early version of the encyclical appeared in the Italian press on Monday, which created a mini-drama about who leaked it and why, and cost the journalist who wrote the introduction his Vatican press credentials.

With the official release set for Thursday at 6 a.m. EDT, this is a good moment for a quick refresher on what an “encyclical” actually is, and why it matters that Francis is devoting one to this subject.

Making the rounds

An encyclical is, literally, a circular letter to be spread through a community. Etymologically, it comes from the Greek word egkyklios, which means “circle.”

Encyclicals are usually addressed to all the bishops of the world, but there are exceptions: Some are addressed to a certain group of bishops (i.e., the bishops of Asia); others specifically to the clergy and all the Catholic faithful.

Still others, such as Pope John XXIII’s 1963 encyclical “Pacem in Terris” (“Peace on Earth”), have been addressed to “all people of good will.”

Beyond containing spelling mistakes and errors in footnotes, the draft version of Laudato Si leaked by the Italian magazine “l’Espresso” on Monday lacked the dedication page, so it’s not yet clear to whom it’s addressed, although in the early version of the text Francis appears to suggest it’s intended for the whole world.

Leaks happen

Despite the frenzy generated by the leak, it’s hardly the first time a news organization published a papal document before its due date.

Pope Benedict XVI’s 2009 encyclical Caritas in Veritate, for example, was largely published before its release by the Italian paper Corriere della Sera. In July 1968, Time’s bureau chief in Rome, Wilton Wynn, “gladly” paid $500 for a leaked copy of Pope Paul VI’s encyclical on birth control, Humanae Vitae.

Technically, Laudato Si will be Francis’ second encyclical letter, but this is the first one he wrote alone. Lumen Fidei was released only three months after he was elected, so it was based on a mostly finished draft from his predecessor. Although uncommon, this wasn’t unprecedented, since Benedict’s first encyclical, Deus caritas est, was partly based on one Pope St. John Paul II had begun but couldn’t finish.

What’s in a name?

The official title of an encyclical is generally formed from the first two or three words of the Latin version, though that’s not the case this time.

Laudato Si, the title chosen by Francis this time, comes from a 13th century prayer written by St. Francis of Assisi called “Canticle of the Creatures,” often referred to as the Canticle of the Sun. It can be translated both as “Be Praised” or “Praised Be,” and it reoccurs several times as the prayer praises God by thanking him for creations such as “Brother Fire” and “Sister Water.”

As a footnote, initial reports said the encyclical would be called “Laudato Sii,” with two i’s, but that’s inaccurate. When the Vatican released the official name, a spokesman explained that the decision was made to use the original form of the poem, which was written in the Umbrian dialect.

Prolific writers

Since the early days of the Church, popes have written various kinds of letters. However, Pope Benedict XIV was the first in modern times to specifically issue a document he called “an encyclical.” That text, Ubi premium, from 1740, dealt with the duties of bishops.

From that moment on, nearly 300 papal encyclicals have been written.

Pope Leo XIII was the most prolific author, with 30 encyclicals written over 25 years. His most famous one, Rerum Novarum (“Of Revolutionary Change”), was promulgated on 1891 and it’s still considered the foundational document of Catholic social teaching.

Authoritative, but not infallible

Although theologians dispute the precise level of authority an encyclical carries, in general the pronouncements in such a text aren’t considered infallible. They generally don’t entail the declaration of a new dogma, meaning a formally defined truth of the faith, although it may contain new doctrines, meaning teachings on faith and morals.

As the Religion News Service explains, that leaves a lot of room for debate, and given the contentious nature of this encyclical, it seems likely that many Catholic interpreters will invoke the traditional phrase “prudential judgment” to describe various aspects of the pope’s argument – meaning, roughly, that his opinion deserves respect, but he could be wrong.

Although Laudato Si is usually referred to as the “eco-encyclical,” the encyclical on “climate change” or Francis’ environmental manifesto, both Francis and the Vatican have said it’s about “the care of our common home” that is “creation.”

On Wednesday, the eve of the official release date, Francis defined the text as an appeal for responsibility to cultivate and protect “the garden in which God has put the human person.”

“This is our home,” Francis said. “It’s crumbling, and this affects us all, specially the poorest ones. Hence, mine is an appeal for responsibility based on what God has told men: care for and preserve creation.”

A wide effect

Laudato Si may be a Church document, but many observers believe it will have a broad cultural impact.

Argentinian climate change expert Pablo Canziani, for instance, says that “undoubtedly” the encyclical will have an impact on the negotiations regarding international policies to fight global warming to be discuss in a United Nations-sponsored meeting in Paris late this year.

A 2007 Nobel Peace Prize winner, Canziani told Crux that the encyclical could provide an ethical and faith-based floor for the implementation of political and technological measures to the fight against climate change.

Canziani also welcomed the impact Francis has had in leaders of other religions to work together on the protection of the environment.

“A technocratic approach isn’t enough to solve socio-environmental problems,” he said.

Other religious leaders also have been emboldened by Laudato Si.

Two days before the encyclical was to appear, Justin Welby, Archbishop of Canterbury and head of the Anglican Church, issued a “green declaration” signed by British faith leaders who assert that climate change has hurt the poor of the world.

On June 15, the Buddhist leader Dalai Lama told his more than 11 million Twitter followers that “since climate change and the global economy now affect us all, we have to develop a sense of the oneness of humanity.”

A day later, the Lausanne Movement, representing Evangelical Christians in almost 200 countries said Evangelicals were anticipating Laudato Si and grateful for it.

A Catholic, an Orthodox, an atheist scientist, and an economist will present Francis’ letter this Thursday in Rome. Francis explained this move on Sunday, saying that “we need unity to protect creation.”