I’m reading John Flavel’s book, Keeping the Heart. The book is a collection of sermons on Proverbs 4:23: “Above all else, guard your heart, for it is the wellspring of life” (NIV).
Flavel pictures the heart as a fort under attack from without and within. It is therefore in need of constant attention and defense:
Lavater on the text will have the word taken from a besieged garrison, beset by many enemies without, and in danger of being betrayed and destroyed by treacherous citizens within, in which danger the soldiers, upon pain of death, are commanded to watch… (p. 2).
We don’t think about our hearts and souls as often as we think about our physical body. But Proverbs 4:23 calls us to constant attention. Guard your heart both from external and internal attacks. Or, as M’Cheyne put it, don’t neglect the “culture of the inner man.”