This morning I was reading Proverbs 4, and spent some time meditating on one of my favorite verses.
Keep your heart with all vigilance, for from it flow the springs of life. (Proverbs 4:23 ESV)
My favorite treatment of this verse, and the idea of "keeping the heart," is John Flavel's wonderful treatise (read it here for free). What does it mean to "keep the heart?"
By keeping the heart, understand the diligent and constant use of all holy means to preserve the soul from sin, and maintain its sweet and free communion with God. [I say constant, for the reason added in the text extends the duty to all the states and conditions of a Christian’s life, and makes it binding always. If the heart must be kept, because out of it are the issues of life, then as long as these issues of life do flow out of it, we are obliged to keep it.] Lavater on the text will have the word taken from a besieged garrison, beset by many enemies without, and in danger of being betrayed by treacherous citizens within, in which danger the soldiers, upon pain of death, are commanded to watch; and though the expression, Keep thy heart, seems to put it upon us as our work, yet it does not imply a sufficiency in us to do it. We are as able to stop the sun in its course, or to make the rivers run backward, as by our own skill and power to rule and order our hearts. We may as well be our own saviors as our own keepers; and yet Solomon speaks properly enough when he says, Keep thy heart, because the duty is ours, though the power is of God; what power we have depends upon the exciting and assisting strength of Christ. Grace within us is beholden to grace without us. “Without me ye can do nothing.” - John Flavel, Keeping the Heart (emphasis mine)