The Law of Undulation

In his book The Screwtape Letters, C.S. Lewis writes from the perspective of a fictional senior demon. Screwtape, who is an instructor to other demons, is corresponding through letters to his nephew and student tempter, Wormwood. The book is packed with insight into how the demonic world strategizes and plans attacks on humanity and the elect saints of God in particular.

In Chapter 8 of the book, Lewis mentions a principle called the “Law of Undulation.” Here is an excerpt from the book:

“Humans are amphibians—half spirit and half animal. (The Enemy’s determination to produce such a revolting hybrid was one of the things that determined Our Father to withdraw his support from Him.) As spirits they belong to the eternal world, but as animals they inhabit time. This means that while their spirit can be directed to an eternal object, their bodies, passions, and imaginations are in continual change, for to be in time means to change. Their nearest approach to constancy, therefore, is undulation—the repeated return to a level from which they repeatedly fall back, a series of troughs and peaks. If you had watched your patient carefully you would have seen this undulation in every department of his life—his interest in his work, his affection for his friends, his physical appetites, all go up and down. As long as he lives on earth periods of emotional and bodily richness and liveliness will alternate with periods of numbness and poverty. The dryness and dullness through which your patient is now going are not, as you fondly suppose, your workmanship; they are merely a natural phenomenon which will do us no good unless you make a good use of it.”

There is much truth to what Lewis describes here. I have seen it play out in my own life many times. Some weeks it seems like I have a handle on sin (whatever that means, I cannot go one day without giving in to it in some way), and others I allow it to beat me down and force me into a corner.

I often feel that my walk with Christ is cyclical, rather than linear. It seems that I reach a certain fellowship or familiarity with Christ, begin to lose focus (much like Peter while he was walking on the water; Matt. 14, Mark 6, John 6), and turn back to sin. Sometimes the return to sin is only for a short time, and other times it is more extended.

This life will consist of periods of undulation; it is unavoidable as long as we are alive. They are a “natural phenomenon” as Lewis called them. The question is: what do we do with them?

Do we allow them to drag us backwards into sin? Do we let depression overcome us, because we feel as though there is no hope? Do we let them throw water on the fire that is the Holy Spirit our gracious God has put inside us to seal us (showing we are His), guaranteeing our inheritance until the day we receive it (Eph. 1:13-14)?

Or, do we run to Christ? Do we get on our knees (literally) and plead with Him to strengthen us, to give us sustaining grace to stand up under the trial (Ps. 18:6)? Do we look our problems in the face and then remind ourselves of the Gospel?

The Gospel says Christ bore the full weight of God’s wrath, hanging between the earth and the sky, so that the record of legal demands against us could be set aside (Col. 2:14). He has borne burdens worse than those we bear, so that we can run to Him in times like this! The Gospel is revitalizing, encouraging, and oh so destructive to sin! It is through the power of the Gospel, and the God-given faith that enables us to participate in it, that we overcome this world (1 Jn. 5:4).

We will have times of trial and seeming spiritual poverty. It is certain. But something else is just as certain. If we belong to Christ, if He has regenerated our hearts, He will keep us by His power. John 10:28 says that we can’t be removed from His hand. His Holy Spirit has sealed us and is our guarantee; He will finish the work He has begun in us (Phil. 1:6).

Don’t lose heart! Remind yourself of the Gospel! Continue pursuing Christ in Scripture, and continue pouring your heart out to Him in prayer. He hears you, and He loves you.

You can get The Screwtape Letters here:

Author’s Note: this is a post specifically about the Law of Undulation in The Screwtape Letters, not a review of The Screwtape Letters which I hope to reread and write about soon!

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