The popularization of this devotion in its modern form is derived from a Roman Catholic nun from France, Margaret Mary Alacoque, who said she learned the devotion from Jesus during a series of apparitions to her between 1673 and 1675,[3] and later, in the 19th century, from the mystical revelations of another Catholic nun in Portugal, Mary of the Divine Heart, a religious sister of the congregation of the Good Shepherd, who requested in the name of Christ that Pope Leo XIII consecrate the entire world to the Sacred Heart of Jesus.

Predecessors to the modern devotion arose unmistakably in the Middle Ages in various facets of Catholic mysticism, particularly with Gertrude the Great.

The wounds and crown of thorns allude to the manner of Christ's passion, while the flames represent a furnace of ardent love.

[8] The revival of religious life and the zealous activity of Bernard of Clairvaux and Francis of Assisi in the twelfth and thirteenth centuries, together with the enthusiasm of the Crusaders returning from the Holy Land, gave a rise to devotion to the Passion of Jesus Christ and particularly to practices in honour of the Sacred Wounds.

The first indications of devotion to the Sacred Heart are found in the eleventh and twelfth centuries in the fervent atmosphere of the Benedictine or Cistercian monasteries.

The earliest known hymn to the Sacred Heart, "Summi Regis Cor Aveto", is believed to have been written by the Norbertine Herman Joseph (d. 1241) of Cologne, Germany.

Among the Franciscans the devotion to the Sacred Heart of Jesus has its champions in Bonaventure (d. 1274) in his Vitis Mystica ("Mystic Vine") and John de la Verna.

His death brings the dead to life, but at his passing heaven and earth are plunged into mourning and hard rocks are split asunder.

This was done so that the Church might be formed from the side of Christ as he slept the sleep of death on the cross, and so that the Scripture might be fulfilled: 'They shall look on him whom they pierced'.

[13]According to Thomas Merton, Lutgarde (d. 1246), a Cistercian mystic of Aywieres, Belgium, was one of the great precursors of the devotion to the Sacred Heart of Jesus.

The idea of hearing the heartbeat of God was very important to medieval saints who nurtured devotion to the Sacred Heart.

[16] Mechtilde reported that Jesus appeared to her in a vision and commanded her to love him ardently, and to honor his sacred heart in the Blessed Sacrament as much as possible.

[18] Book 2 of the Herald of Divine Love (Latin: Legatus divinæ pietatis) vividly describes Gertrude's visions, which show a considerable elaboration on the hitherto ill-defined veneration of Christ's heart.

The women of Helfta – Gertrude foremost, who surely knew Bernard's commentary, and to a somewhat lesser extent the two Mechthildes – experienced this devotion centrally in their mystical visions.

[23] Margaret Mary also said that she was instructed to spend an hour every Thursday night, from eleven to midnight, to pray and meditate on Jesus' agony in the Garden of Gethsemane.

Her prayers intended to ask mercy for sinners as well as to make reparation for the abandonment Jesus felt from his apostles in the garden.

"[25] He then asked Margaret Mary for a feast of reparation of the Friday after the octave of Corpus Christi, bidding her consult her confessor Claude de la Colombière, then superior of the small Jesuit house at Paray-le-Monial.

After his death on 15 February 1682, his journal of spiritual retreats was found to contain a copy in his handwriting of the account that he had requested of Margaret Mary, together with a few reflections on the usefulness of the devotion.

Based on the messages she said she received in her revelations of Christ, on 10 June 1898 her confessor at the Good Shepherd monastery wrote to Pope Leo XIII stating that Mary of the Divine Heart had received a message from Christ, requesting the pope to consecrate the entire world to the Sacred Heart.

The following day, in Annum sacrum, Pope Leo XIII consecrated the entire world to the Sacred Heart of Jesus.

The outcome of this investigation was positive, and in 1899 he decreed that the consecration of the entire human race to the Sacred Heart of Jesus should take place on 11 June 1899.

Pius X also granted a Pontifical decree for the imposition of a golden crown to the lowly foot of a statue of the Sacred Heart of Jesus in the Nevers Cathedral on 9 July 1908 (via the Archbishop of Nevers and Besancon, Francois Leon Gauthey, both signed and notarized by the Sacred Congregation of Rites).

[32] His encyclical letter Miserentissimus Redemptor (1928) reaffirmed the importance of consecration and reparation to the Sacred Heart of Jesus.

[36] On 25 March 1874, by petition of president Gabriel García Moreno and archbishop José Ignacio Checa y Barba, Ecuador was the first country in the world to be consecrated to the Sacred Heart by legislative decree.

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.

A personal prayer of consecration to the Sacred Heart was written by Saint Margaret Mary Alacoque,[55] allegedly under the inspiration of Jesus, which she wrote to the priest John Croiset, recommending that he include it in the book he was to publish about her revelations "It comes from Him, and He would not agree to its omission.

If the need arises, in order to receive communion in a state of grace, a person should also make use of the sacrament of penance before attending Mass.

[60] Alacoque stated that she received a vision of Jesus in which she was instructed to spend an hour every Thursday night as a reparation and to pray and meditate on his agony in the Garden of Gethsemane.

The Sacred Heart crowned with thorns is depicted on the reverse side of the Miraculous Medal,[77] The Carillon-Sacré-Coeur flag has been adopted by the Société Saint-Jean-Baptiste in Québec.

However, the Sacred Congregation of Rites stated in 1879 that images of the hearts of Jesus or Mary were not appropriate for being placed on the altar for Mass, although are appropriate for "private devotion".