Francis has drawn from a wide variety of sources, partly to buttress his arguments, partly to underscore the universality of his message. He regularly cites passages from his two predecessors, Pope John Paul II and Pope Benedict XVI, even as he also draws prominently from his religious ally, Patriarch Bartholomew I of Constantinople, leader of the world’s Eastern Orthodox Christians. He also cites a Sufi Muslim mystic, Ali al-Khawas.

Francis begins the encyclical with a hymn written by St. Francis of Assisi, the 13th-century friar who is the patron saint of animals and the environment. Francis cites the Bible’s book of Genesis to underpin his theological argument, though in a passage certain to rankle some Christians, he chastises those who cite Genesis as evidence that man has “dominion” over earth and therefore an unlimited right to its resources. Some believers have used this biblical understanding of “dominion” to justify practices such as mountaintop mining or fishing with gill nets.