Pope Leo XIII (2 March 1810 – 20 July 1903), born Vincenzo Gioacchino Raffaele Luigi Pecci to an Italian comital family, was the 256th Pope of the Roman Catholic Church, reigning from 1878 to 1903. He was the oldest pope (reigning until the age of 93), and had the third longest pontificate, behind his immediate predecessor Pius IX and John Paul II.

He is known for intellectualism, the development of social teachings with his encyclical Rerum Novarum and his attempts to define the position of the Church with regard to modern thinking. He influenced Roman Catholic Mariology and promoted both the rosary and the scapular. He issued a record eleven encyclicals on the rosary, approved two new Marian scapulars and was the first Pope to fully embrace the concept of Mary as mediatrix.

Born in Carpineto Romano, near Rome, he was the sixth of the seven sons of Count Ludovico Pecci and his wife Anna Prosperi Buzzi. Until 1818 he lived at home with his family, "in which religion counted as the highest grace on earth, as through her, salvation can be earned for all eternity". Together with his brother he studied in the Jesuit College in Viterbo, where he stayed until 1824. He enjoyed the Latin language and was known to write his own Latin poems at the age of eleven.

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.