2563 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.
Catechism of the Catholic Church