In January 1942, as German bombers were terrorizing British cities, C. S. Lewis took the gospel to the airwaves, appearing repeatedly on the BBC’s religious programs (the talks were later collected in the book Mere Christianity). Increasing fame, however, did not diminish Lewis’s willingness to answer the many letters he received, many as a result of his radio talks. Here he counsels a former student who is experiencing a “trough” – a time of personal difficulties.

Dear Mrs. Neylan,

Sorry you’re in a trough. I’m just emerging (at least I hope I am) from a long one myself. As for the difficulty of believing it is a trough, one wants to be careful about the word “believing.” We often mean by it “having confidence or assurance as a psychological state” – as we have about the existence of furniture. But that comes and goes and by no means always accompanies intellectual assent. For example, in learning to swim you believe, and even know intellectually, that water will support you, long before you feel any real confidence in the fact. ... 

In the meantime, as one has learnt to swim only by acting on the assent in the teeth of all instinctive conviction, so we shall proceed to faith only by acting as if we had it. Adapting a passage in The Imitation of Christ [Thomas à Kempis], one can say: “What would I do now if I had a full assurance that there was only a temporary trough,” and having got the answer, go and do it. 

I am a man, and therefore lazy: you a woman, therefore probably a fidget. So it may be good to advise you (though it would be bad to me) not even to try to do in the trough all you can do on the peak. ...

I know all about the despair of overcoming chronic temptations. It is not serious, provided self-offended petulance, annoyance at breaking records, impatience, etc. doesn’t get the upper hand. No amount of falls will really undo us if we keep on picking ourselves up each time. 

We shall of course be very muddy and tattered children by the time we reach home. But the bathrooms are all ready, the towels put out, and the clean linen clothes are in the airing cupboard. The only fatal thing is to lose one’s temper and give up. It is when we notice the dirt that God is most present to us: it is the very sign of his presence.

Taken from The Collected Letters of C. S. Lewis, volume 2, ed. Walter Hooper (Harper San Francisco, 2005), 506–507. Copyright © 2004 by C.S. Lewis Pte. Ltd. Extract reprinted by permission.