Keep thy heart with all diligence; for out of it are the issues of life.
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Proverbs 4:21-25
Tyndale Open Study Notes (CC BY-SA 4.0).
4:23 In the Old Testament, the heart represents the center of emotions, thinking, and reasoning (e.g., Gen 6:5; Deut 4:29; Ps 131:1). The heart is crucial in the battle between wisdom and foolishness, between righteousness and evil (see Matt 5:8; 13:15; John 12:40; Rom 6:17).
Other Bible passages linked to this one, most cited first.
A good man out of the good treasure of his heart bringeth forth that which is good; and an evil man out of the evil treasure of his heart bringeth forth that which is evil: for of the abundance of the heart his mouth speaketh.
O generation of vipers, how can ye, being evil, speak good things? for out of the abundance of the heart the mouth speaketh. A good man out of the good treasure of the heart bringeth forth good things: and an evil man out of the evil treasure bringeth forth evil things.
For from within, out of the heart of men, proceed evil thoughts, adulteries, fornications, murders, Thefts, covetousness, wickedness, deceit, lasciviousness, an evil eye, blasphemy, pride, foolishness: All these evil things come from within, and defile the man.
Search me, O God, and know my heart: try me, and know my thoughts: And see if there be any wicked way in me, and lead me in the way everlasting.
He that keepeth his mouth keepeth his life: but he that openeth wide his lips shall have destruction.
The heart is deceitful above all things, and desperately wicked: who can know it?
Authorship: the book itself or Christian tradition. Approximate dates, as in Carson and Moo, An Introduction to the New Testament, and Longman and Dillard, An Introduction to the Old Testament.