The heart is the fountain or wellspring of life. It contains the essence of who we are so that’s why God has chosen to live within our hearts. Because it is the place where God has chosen to meet with us, it’s critical that we guard our hearts.
Religion by its nature is an enemy of the heart because it attacks it by telling us that our hearts are wicked and can’t be trusted. This creates insecurity because it causes us to distrust the voice of God who speaks to us from our heart. This false teaching is actually based on an Old Covenant verse which doesn’t apply to us today. Instead as children of God under a new covenant, we’ve been given a new heart which is infused with the life of God.