Proverbs 4:23 says Keep thy heart with all diligence; For out of it are the issues of life; The heart is the foundation of all our virtue and values, the heart dictates to our mind who we are. The heart sets the boundaries of what our mind can think and dream. These boundaries are created from our core values, integrity, purity, holiness, etc. The righteousness of Christ in us, is the boundary are mind's should have.