The word heart appears eight-hundred fifty times in the Ancient Testament and one hundred fifty nine in the New, of which ninety one are in the Writings of St. Paul.
Often the word heart refers to the heart of God as well as to the heart of man.
Sometimes, it refers to the vital organ of the human being, but most often it appears with a symbolic meaning, that is, that which is most intimate.
With a symbolic meaning, it can refer either to the heart of God or to the heart of man.
When it refers to God, it is, almost always, to show His love and His mercy towards His people (Cf. Jer 32, 40-41).
When it refers to man, it is to tell us that which is in his interior, the unifying center of his being, whence proceed the decisions and, consequently, his exterior acts.
In Sacred Scripture heart stands for man.
It is in the heart that the Bible places the intellectual life, the capacity to know. Therefore, the heart is intelligent, wise. One prays with the heart (Dt 29, 3; Is 6, 10; Mt 13, 15; Mk 7, 21).
Also in the Bible, the word heart is the center of the moral and ethical dimensions; hence we find some passages that say that man has a humble, meek, pure, straight, merciful heart (Cf. Ex 10, 20: Prov 6, 14; Jer 17, 9; Mt 5, 8; Rom 1, 24).
In Sacred Scripture, the affective life is also described using the word heart; it is a heart that suffers, gets anxious, rejoices, feels sorrow, etc. (Cf. Gen 6, 6; Is 7, 4; Lk 24, 32; Rom 9, 2).
The first Commandment tells us that the biblical love is activity of the heart: “Thou shall love the Lord thy God with all thy heart”. Conversion is also activity of the heart: “I will change your hearts of stone into hearts of flesh”.
In the Gospels, the word heart takes on a deeper meaning. It tells us about the interior, the center of love.
It is the Lord Himself Who tells us: “Learn from Me, for I am meek and humble of heart”.
Throughout these texts, we catch a glimpse of His intimacy, of His piety, of His compassion; we see how He rejoices, gets surprised, feels sorrow.
We discover, moreover, that His Heart loves passionately: “Having loved his own, He loved them until the end” (Jn 13, 1).