Our hearts are deceitful, but God knows our hearts inside out. He has made our hearts new. The labyrinth belongs to him now and he is gradually remodelling it into a beautiful place where sin cannot hide.  And if you want to know the true state of your heart, the Lord will help you. Ps 139.23f: Search me, O God, and know my heart! Try me and know my thoughts! ²⁴And see if there be any grievous way in me, and lead me in the way everlasting!

In Proverbs 4.23 Solomon warns his son, ‘Keep your heart with all vigilance, for from it flow the springs of life.’ He goes on to give admonitions about the mouth, the eyes and the feet (vv24-27), but it is the heart that must be guarded above all else. Why?

In Scripture, the word ‘heart’ is used more than 1000 times, but it almost never refers to the physical organ inside our chests. The Theological Wordbook of the Old Testament sums up all the usages of the term in this way: it is ‘the richest, most all-encompassing biblical term for the totality of a man’s inner nature.’ The heart is said to do a wide range of things in the Bible, but all its many activities fall into one of the three main faculties of the soul: the mind, the affections and the will. It includes the mind—our thoughts, imagination, fantasies, judgments and attitudes. It encompasses the affections—our emotions, our desires and longings, our revulsions. And it describes the will—our choices, decisions and motivations.

Once we understand that the heart involves all these things, it becomes even clearer why we must guard it with all vigilance, before all else—because it is so fundamental. It is the control centre of the whole person. Indeed Scripture sometimes uses ‘heart’ as a kind of synonym for the self (e.g. Gen 18.5; Ex 9.14; 1Pt 3.4: ‘…the hidden person of the heart’.)

We also need to guard our hearts with all vigilance because they are under constant attack. From the world and the devil outside ourselves of course, but also—most dangerously of all—from an enemy within: the flesh—a traitor inside our own hearts, a Judas looking for an opportune moment to hand us over to sin. The heart is deceitful above all things, and desperately sick; who can understand it? (Jer 17.9). It is like an unsearchable labyrinth, with endless twists and turns, blind alleys and dark corners where the Minotaur of our indwelling sin lurks in wait for us.

We need to guard our hearts too because the Lord wants our hearts. Prov 23.6: My son, give me your heart. What a beautiful and powerful incentive this is! We are keeping our hearts for our Father! We wouldn’t be satisfied with a marriage where our spouse was dutiful and faithful outwardly, but longed inwardly to be with someone else to whom their heart belonged. Why would God be content with that from us? He wants our hearts—our minds, our affections and our wills. The totality of our inner nature and not just our outward behaviour. Isa 29.13: And the Lord said: “…this people draw near with their mouth and honor me with their lips, while their hearts are far from me… Ps 51.16f: For you will not delight in sacrifice, or I would give it; you will not be pleased with a burnt offering. The sacrifices of God are a broken spirit; a broken and contrite heart, O God, you will not despise.

How then do we do this vital work of guarding our hearts? The first step is to do a ‘spiritual MRI scan’ of our hearts. We need to know the current state of our hearts so that we can address the problems and weaknesses we find. Rom 12.3 tells us to ‘think [of ourselves] with sober judgment.’ The Puritan John Flavel, in an exposition of Prov 4.23, wrote these challenging words: ‘Some people have lived forty or fifty years and have had scarcely one hour’s discourse with their own hearts! … Of all works in religion, this is the most difficult, constant and important work. Heart work is indeed hard work. To shuffle over religious duties with a loose and heedless spirit will cost no great pains. But to set yourself before the Lord and tie up your loose and vain thoughts to a constant and serious attention upon him, this will cost you something.’ John Owen in his book The Mortification of Sin advises his readers: “Be acquainted, then, with thine own heart: though it be deep, search it; though it be dark, inquire into it; though it give all its distempers other names than what are their due, believe it not.”

As we carry out this spiritual MRI scan of our hearts we need to bear in mind what the heart is—the totality of our inner nature: the mind, will and affections. We need to assess all three areas of the heart with probing diagnostic questions. Here are some examples of what that might look like:

A. The mind (thoughts, attitudes, imagination, plans, judgments, discernment).

a) What do you think about? Do you think about spiritual things? The glory of God? The Person and work of Jesus Christ? The Gospel of grace? Sinclair Ferguson once asked the unsettling question, ‘How many Christians today could sit in a room without any resources and think about Jesus Christ for more than five minutes before they run dry?’

b) What do you think about when you’re not focused on specific tasks? John Owen calls these ‘Natural, voluntary thoughts’. They’re like the screensaver that comes up on our computer screens. When the computer is idling for more than a few minutes, it’s the image that appears. What images appear in your mind when it’s not actively engaged in a particular task? Owen says, ‘These thoughts give the best measure of the frame of our minds and hearts… such as the mind of its own accord is apt for, inclines & ordinarily betakes itself unto.’ In other words, do you think about spiritual things when you’re not forced to because you’re listening to a sermon in church or taking part in a Bible study?

c) Owen also asks, do you abound in spiritual thoughts? What proportion of your thoughts are spiritual compared to your thoughts about other things? Here’s a very challenging way of asking the question: do spiritual thoughts ever distract you when you’re engaged in other pursuits? We all know what it’s like to be distracted by earthly thoughts intruding when we’re trying to pray or read the Bible in our daily devotions or listen to a sermon, but is it ever the other way around? Do you ever find yourself thinking about the Lord Jesus when you’re in the middle of watching a film or a football match?

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