The foundation for the Sacred Heart devotion began in early Christianity. Sacred Scripture, particularly the New Testament, mentions the love of God many times, and the Church Fathers discuss God’s love as well.
In the eleventh century, Christians often meditated on the Five Wounds of Jesus, and the specific devotion to the Sacred Heart came from this meditation. St. Gertrude the Great, who had private revelations regarding the Sacred Heart, helped further the understanding of Jesus’ Sacred Heart in the late 13th-century.
Several centuries later, in 1670, St. John Eudes celebrated the first Feast of the Sacred Heart. In 1673, St. Margaret Mary Alacoque, a French Visitation nun, received her own revelations, in which Jesus explained His love for all people, even allowing St. Margaret to lay her head on His Heart, as He had also allowed St. Gertrude to do. He asked that Catholics receive Holy Communion on the First Fridays of the month and adore Him in the Holy Eucharist.
In 1675, Jesus told St. Margaret that He wanted an annual feast in honor of His Sacred Heart. In 1856, Blessed Pope Pius IX designated that the Feast of the Sacred Heart would be celebrated universally on the Friday after the Corpus Christi octave each year.