Proverbs 4:23

Keep thy heart with all diligence The Hebrew is, Above all keeping, keep thy heart, that is, thy mind and thoughts, thy will and affections, which are the more immediate cause of men's actions. Out of it are the issues of life The life or death of the soul proceeds from the heart: an upright, enlightened, renewed, devout, and watchful heart gives birth to those holy dispositions, words, and actions, which manifest spiritual life, and lead to eternal life: on the contrary, a heart insincere, unenlightened, unrenewed, and corrupt, without knowledge, without grace, produces those tempers, words, and works, which imply spiritual death, and lead to eternal death. From the heart proceeds all evil, Matthew 15:11. Guard it therefore most carefully, with every kind of diligence, and above all other cares.