The heart symbolizes the center or "core" of our being, from which prayer and moral actions originate.
The heart is mentioned frequently in the Bible, especially in the New Testament, where Jesus frequently uses the term to explain spiritual truths.
Blessed are the clean of heart, for they will see God. (Matthew 5:8)For where your treasure is, there also will your heart be. (Matthew 6:21)You shall love the Lord your God with all your heart, with all your soul, with all your mind, and with all your strength. (Mark 12:30)
In Christianity, the heart symbolizes the center or core of our being, from which prayer and moral actions originate. This even explains the word “core,” which is derived from the Latin word cor, meaning, “heart.”
The Catechism of the Catholic Church echoes this definition and describes the spiritual meaning of the heart in its section on prayer.
Where does prayer come from? Whether prayer is expressed in words or gestures, it is the whole man who prays. But in naming the source of prayer, Scripture speaks sometimes of the soul or the spirit, but most often of the heart (more than a thousand times). According to Scripture, it is the heart that prays. If our heart is far from God, the words of prayer are in vain.The heart is the dwelling-place where I am, where I live; according to the Semitic or Biblical expression, the heart is the place “to which I withdraw.” The heart is our hidden center, beyond the grasp of our reason and of others; only the Spirit of God can fathom the human heart and know it fully. The heart is the place of decision, deeper than our psychic drives. It is the place of truth, where we choose life or death. It is the place of encounter, because as image of God we live in relation: it is the place of covenant. (CCC 2562-2563)
Besides prayer, the heart is also seen as a source of our moral decisions.
The heart is the seat of moral personality: “Out of the heart come evil thoughts, murder, adultery, fornication” … The “pure in heart” are promised that they will see God face to face and be like him. Purity of heart is the precondition of the vision of God. Even now it enables us to see according to God, to accept others as “neighbors”; it lets us perceive the human body – ours and our neighbor’s – as a temple of the Holy Spirit, a manifestation of divine beauty…Purity of heart requires the modesty which is patience, decency, and discretion. Modesty protects the intimate center of the person. (CCC 2517, 2519, 2533)
This is why the heart is so often used in spiritual writings, as it is seen as a primary source of so much that happens in our spiritual lives. It also explains why love is associated with the heart, as authentic love comes from the “core” of our being, not something that is on the “surface.”
For this same reason, it is significant that Jesus is often depicted holding out his heart to us, inviting us to take it within ourselves and let Jesus’ heart rule over our heart.
As Jesus said to his disciples, “Take my yoke upon you and learn from me, for I am meek and humble of heart; and you will find rest for yourselves” (Matthew 11:29).
If we want to progress in the spiritual life, we need to look at our heart and let God transform it, thus transforming our prayer and moral decisions.
The unique symbolism of the Sacred Heart