Esperanto has served an important role in several religions, such as Oomoto from Japan and Baha'i from Iran, and has been encouraged by others.
The Oomoto religion encourages the use of Esperanto among their followers and includes Zamenhof as one of its deified spirits.
The Bahá'í Faith encourages the use of an auxiliary international language. While endorsing no specific language, some Bahá'ís see Esperanto as having great potential in this role.
Lidja Zamenhof, the daughter of Esperanto founder L. L. Zamenhof, became a Bahá'í.
Various volumes of the Bahá'í literatures and other Baha'i books have been translated into Esperanto.
Esperanto is also actively promoted, at least in Brazil, by followers of Spiritism. The Brazilian Spiritist Federation publishes Esperanto coursebooks, translations of Spiritism's basic books, and encourages Spiritists to become Esperantists.
The first translation of the Bible into Esperanto was a translation of the Tanach or Old Testament done by L. L. Zamenhof. The translation was reviewed and compared with other languages' translations by a group of British clergy and scholars before publishing it at the British and Foreign Bible Society in 1910. In 1926 this was published along with a New Testament translation, in an edition commonly called the "Londona Biblio". In the 1960s, the Internacia Asocio de Bibliistoj kaj Orientalistoj tried to organize a new, ecumenical Esperanto Bible version. Since then, the Dutch Lutheran pastor Gerrit Berveling has translated the Deuterocanonical or apocryphal books in addition to new translations of the Gospels, some of the New Testament epistles, and some books of the Tanakh or Old Testament. These have been published in various separate booklets, or serialized in Dia Regno , but the Deuterocanonical books have appeared in recent editions of the Londona Biblio.
Two Roman Catholic popes, John Paul II and Benedict XVI, have regularly used Esperanto in their multilingual urbi et orbi blessings at Easter and Christmas each year since Easter 1994. Christian Esperanto organizations include two that were formed early in the history of Esperanto, the International Union of Catholic Esperantists and the International Christian Esperantists League. An issue of "The Friend" describes the activities of the Quaker Esperanto Society. There are instances of Christian apologists and teachers who use Esperanto as a medium. Nigerian Pastor Bayo Afolaranmi's "Spirita nutraĵo" (spiritual food) Yahoo mailing list, for example, has hosted weekly messages since 2003. Chick Publications, publisher of Protestant fundamentalist themed evangelistic tracts, has published a number of comic book style tracts by Jack T. Chick translated into Esperanto, including "This Was Your Life!" ("Jen Via Tuto Vivo!")
Ayatollah Khomeini of Iran called on Muslims to learn Esperanto and praised its use as a medium for better understanding among peoples of different religious backgrounds. After he suggested that Esperanto replace English as an international lingua franca, it began to be used in the seminaries of Qom. An Esperanto translation of the Qur'an was published by the state shortly thereafter. In 1981, Khomeini and the Iranian government began to oppose Esperanto after realising that followers of the Bahá'í Faith were interested in it.