A sacred language, "holy language" (in religious context), or liturgical language, is a language that is cultivated for religious reasons by people who speak another language in their daily life.

Once a language becomes associated with religious worship, its believers often ascribe virtues to the language of worship that they would not give to their native tongues.^{[citation needed]} In the case of sacred texts, there is a justified fear of losing authenticity and accuracy by a translation or re-translation, and difficulties in getting general acceptance for a new version of a text. The sacred language is typically vested with a solemnity and dignity that the vernacular lacks. Consequently, the training of clergy in the use of the sacred language becomes an important cultural investment, and their use of the tongue is perceived to give them access to a body of knowledge that untrained lay people cannot (or should not) access. In medieval Europe, the (real or putative) ability to read (see also benefit of clergy) scripture—which was in Latin—was considered a prerogative of the priesthood, and a benchmark of literacy; until near the end of the period almost all who could read and write could do so in Latin.

The Sacred Heart (also known as Most Sacred Heart of Jesus) is one of the most famous religious devotions to Jesus' physical heart as the representation of his divine love for humanity.

This devotion is predominantly used in the Catholic Church and among some high-church Anglicans and Lutherans. The devotion especially emphasizes the unmitigated love, compassion, and long-suffering of the heart of Christ towards humanity. The origin of this devotion in its modern form is derived from a French Roman Catholic nun, Marguerite Marie Alacoque, who said she learned the devotion from Jesus during a mystical experience. Predecessors to the modern devotion arose unmistakably in the Middle Ages in various facets of Catholic mysticism.

In the Roman Catholic tradition, the Sacred Heart has been closely associated with Acts of Reparation to Jesus Christ. In his encyclical Miserentissimus Redemptor, Pope Pius XI stated: "the spirit of expiation or reparation has always had the first and foremost place in the worship given to the Most Sacred Heart of Jesus". The Golden Arrow Prayer directly refers to the Sacred Heart.