Assurance of salvation is God’s will for Christians. A continual lack of assurance and doubting of one’s standing before God may appear ultra-spiritual, but it is actually a sign of spiritual immaturity. Scripture repeatedly calls Christians to pursue assurance and assumes that it is possible to attain it.
And we desire each one of you to show the same earnestness to have the full assurance of hope until the end, so that you may not be sluggish, but imitators of those who through faith and patience inherit the promises (Heb 6:11-12; emphasis addded)
I write these things to you who believe in the name of the Son of God that you may know that you have eternal life. (1 John 5:13; emphasis added)
Assurance of salvation must be ultimately grounded in God’s work in Christ and his unshakable promises to keep his children in the faith (John 10:27-30; Romans 8:28-39). Yet, pursuing obedience more than introspection is another vital key to assurance, while understanding the weight we should ascribe to each aspect of our assurance (e.g, God’s work in Christ, his unfailing promises, the Spirit’s inner-testimony, our own faith and obedience) is essential too.
There is, however, one area of our spiritual life that is sometimes overlooked in our quest for assurance. And I believe this area is overlooked precisely because it does not appear spiritual at all. Because we are a composite of material and immaterial, our bodies will affect our souls, and our souls will affect our bodies (e.g., Psalm 32:3-4). When it comes to assurance, we may find that adequate sleep and exercise may be exactly what we need. Concerning sleep, consider these words from D. A. Carson as he discusses the reasons for why one may struggle with doubts about Jesus’ resurrection:
Doubt may be fostered by sleep deprivation. If you keep burning the candle at both ends, sooner or later you will indulge in more and more mean cynicism—and the line between cynicism and doubt is a very thin one. Of course, different individuals require different numbers of hours of sleep: moreover, some cope with a bit of tiredness better than others. Nevertheless, if you are among those who become nasty, cynical, or even full of doubt when you are missing your sleep, you are morally obligated to try to get the sleep you need. We are whole, complicated beings; our physical existence is tied to our spiritual well-being, to our mental outlook, to our relationships with others, including our relationship with God. Sometimes the godliest thing you can do in the universe is get a good night’s sleep—not pray all night, but sleep. I’m certainly not denying that there may be a place for praying all night; I’m merely insisting that in the normal course of things, spiritual discipline obligates you get the sleep your body need (Scandalous: The Cross and Resurrection of Jesus, 147)
What about exercise? Scripture doesn’t say much about it, and when it does, it is clear that “physical discipline” is of less value than training oneself for godliness (1 Tim 4:7-8). What we must keep in mind, however, is that during the time both the Old and New Testaments were penned, there was little need to exhort people to exercise because regular physical activity was woven into daily life. Because much of our work in the 21st century is mostly sedentary, and cars and buses and trains decrease the need to walk from one place to another, we must intentionally pursue cardio-vascular and muscular exercise for the sake of our health–physical health, of course, but spiritual health as well. Consider these words from Donald Whitney regarding exercise:
One of the ways the body can have a positive effect upon the soul is through recreational physical activity. Because most spiritual practices are by definition spiritual and not very physical, if our daily work is mostly mental and sedentary then there’s little diversity in he kind of stimuli we experience. And the monotony of that can lessen the impact of our spiritual practices. The variety that recreational physical activity provides to the brain cells and muscle fibers of a body may help to refresh the soul that dwells in it. . . . (Simplify Your Spiritual Life, 2003, 159-60)
Whitney doesn’t speak directly toward assurance, but his point–that physical activity affects our spiritual condition–does have bearing on the issue. Like a lack of sleep can increase opportunity for doubts to creep into a tired, unguarded mind (see Carson’s quote above), so a lack of exercise can contribute to spiritual dryness and dullness.
Of course, there is always the danger of giving too much time and attention to sleep and physical exercise. Scripture is clear that laziness is contrary to our design and God’s will for our lives, so indulgence in sleep should be avoided (see Prov 12:11, 27; 13:4; 19:15, 24; 20:4; 21:5; 26:15 20:4; 21:5; 24:33-34). And we may be called to give up our health for the sake of Christ (Luke 9:25; 2 Cor 6:3-10; 11:23-27).
We take care of our bodies through regular sleep and exercise, therefore, not to attain peak physical shape, but to maintain a clear sight of Jesus and the assurance of our final salvation so that we might labor diligently during our short time on earth. John Piper says it well: “It may seem paradoxical, but that’s the way it is: The right use of your body and your mind may enable you to see so much of God that you would sacrifice your life for Christ” (When I Don’t Desire God, 203). So, in your pursuit of full assurance, get some sleep, get some exercise, and be willing to lay down both for the sake of Jesus.