Jesus, who is one with the Father (cf. John 10, 30), invites his disciples to live in close communion with him, to model their lives on him and on his teaching. He, in turn, reveals himself as “meek and humble of heart” (Matthew 11, 29). It can be said that, in a certain sense, devotion to the Sacred Heart of Jesus is a cultic form of the prophetic and evangelic gaze of all Christians on him who was pierced (cf. John 19, 37; Zac 12, 10), the gaze of all Christians on the side of Christ, transfixed by a lance, and from which flowed blood and water (cf. John 19, 34), symbols of the “wondrous sacrament of the Church” (St. Augustine).
The Gospel of St. John recounts the showing of the Lord’s hands and his side to the disciples (cf. John 20,20), and of his invitation to Thomas to put his hand into his side (cf. John 20, 27). This event has also had a notable influence on the origin and development of the Church’s devotion to the Sacred Heart.
These and other texts present Christ as the paschal Lamb, victorious and slain (cf. Apoc 5,6). They were objects of much reflection by the Fathers who unveiled their doctrinal richness. They invited the faithful to penetrate the mysteries of Christ by contemplating the wound opened in his side. Augustine writes:
“Access is possible: Christ is the door. It was opened for you when his side was opened by the lance. Remember what flowed out from his side: thus, choose where you want to enter Christ. From the side of Christ as he hung dying upon the Cross there flowed out blood and water, when it was pierced by a lance. Your purification is in that water, your redemption is in that blood”.
Excerpted from the Directory on Popular Piety and the Liturgy