Sacred Heart, also called Sacred Heart of Jesus, in Roman Catholicism, the mystical-physical heart of Jesus as an object of devotion. In addition to a feast, now celebrated on the Friday of the third week after Pentecost, devotion includes acts of consecration and honour given to the image of the Sacred Heart. The use of Jesus’ heart to symbolize his love for humanity is not found in the Bible but in the writings of some medieval mystics.
We say, “I put my heart into it” and “I want that with all my heart.” The heart also is a symbol for love, perhaps because it seems to beat faster when we are in love. The biblical image of the heart means the depth of our selves where we decide for or against God.
According to the Gospel of John, after Jesus had died a soldier made sure of his death by piercing his side with a lance. Blood and water ran out (19:34). Jesus’ pierced heart became a sign of the completeness of his love for us, a love that compelled him to die for us and that prompted him to remain with us in the bread and wine of the Eucharist. The physical heart of Jesus is the symbol of the total love of Jesus, divine and human.
The Heart of Christ summarizes the paschal mystery—the death and resurrection of Jesus that were prompted by divine love.
Written by: Rosemary
Reference: https://www.loyolapress.com/our-catholic-faith/scripture-and-tradition/devotions/the-sacred-heart