Father Leo John Dehon, the founder of the Priests of the Sacred Heart, maintained a deep devotion to the Sacred Heart of Jesus. He chose St. John as a patron saint of his Congregation because St. John sat close to Jesus at the Last Supper and wrote about the pierced side of Christ in his Gospel:

So the soldiers came and broke the legs of the first and then of the other one who was crucified with Jesus. But when they came to Jesus and saw that He was already dead, they did not break His legs. However, one of the soldiers pierced His side with a lance; and immediately there came out blood and water. He who saw it has testified and his testimony is true - he knows that he tells the truth - in order that you may believe. For this happened so that the Scripture passage might be fulfilled: they will look upon Him whom they have pierced. (John 19:32-37)

Devotion to the Sacred heart is as old as the Church herself. The image of Christ hanging on the Cross with blood and water flowing from His side made a tremendous impression on early Christians. St. Irenaeus, who lived at the turn of the third century, wrote: "The church is the source of living water which flows from the Heart of Christ."

In the centuries which followed, many saints meditated on the pierced side of Christ. The Heart of Jesus became for them a wonderful sign of God's infinite love and mercy. St. Bernard, St. Bonaventure, St. Gertrude, St. Catherine of Sienna, and St. Francis of Assisi, all spoke of God's great love for us. St. Bonaventure, reflecting on God's love and our need to return His love, wrote:

My soul, if the voice of your beloved makes you melt into love for Him, why are you not utterly inflamed and consumed when you enter by the sacred wound of His side into the burning furnace of His loving Heart.

St. Gertrude also spoke of this great love and reflected on the Sacred Heart as a way of preparing for her death:

God of my heart, wash and wipe away by the burning love of Your pierced Heart all the stains of my guilty heart... so that Your bitter passion may serve as a shelter at the hour of my death and that Your gentle Heart, broken for love of me, may be my eternal dwelling, since I love You alone more than all creatures in the world.

St. John Eudes dedicated almost his entire life to preaching about God's love revealed in the pierced side and Heart of Christ. He wrote:

My Savior, what made You suffer so many torments if it was not Your infinite love for Your Father and for us? We can say that You died of loving sorrow and that Your Heart has been torn and broken by sorrowing love for the glory of the Father and for our redemption.

Perhaps the most recognized saint in the Church regarding the Sacred Heart is St. Margaret Mary Alacoque. She was a nun of the Visitation Order, living in a cloister in Paray-le-Monial, France. In the years between 1673 and 1675, she experienced many visions of the Sacred Heart. She saw His Heart engulfed in flames and surrounded by thorns and heard His gentle companies:

Behold this Heart, which has loved so much but has received nothing but coldness, indifference, and ingratitude in return.

St. Margaret Mary understood the infinite love which the Sacred Heart symbolized. She responded to this love with a desire to "make-up" for the lack of love which was shown to Him. This is the meaning she gave to reparation.

From her cloister, St. Margaret Mary promoted the Feast Day of the Sacred Heart, First Friday Devotions, and the Holy Hour of Reparation. She is perhaps best known for the Twelve Promises of the Sacred Heart which she received in her visions.

Closer to our time, many Popes have responded to God's love as it has been revealed in the Sacred Heart of His Son. In 1899, Pope Leo XIII consecrated the entire world to the Sacred heart. In 1956, Pope Pius XII wrote an encyclical letter on the Sacred Heart. And more recently, Pope John Paul II spoke the following words to pilgrims in St. Peter's Square:

The Son Himself became man, and as such He had a human heart, with which He loved and responded to love - first of all to the Father's love. Therefore on this Heart, on the Heart of Jesus, the Father's pleasure is concentrated. It is a salvific pleasure. Through it, the Father embraces in the Heart of His son everyone for whom this Son became man; everyone for whom He has a Heart; everyone for whom He died and rose. In the Heart of Jesus mankind and the world rediscovers the Father's pleasure. This is the Heart of our Redeemer; it is the Heart of the Redeemer of the world.

Devotion to the Sacred Heart deals with matters of the heart which call us to a deeper commitment to Christ and to others. Christ's love becomes our love. His mission becomes our mission, the work of redemption.

As Father Dehon wrote:

Devotion to the Sacred Heart begins in the interior life of souls and is destined to penetrate into the social life of people. For us, it is not a simple devotion. It is indeed a renewal of the whole of the Christian Life.