'I do get that sudden feeling that the whole thing is hocus pocus and it now worries me hardly at all. Surely the mechanism is quite simple? Sceptical, incredulous, materialistic ruts have been deeply engraved in out thought, perhaps even in our physical brains by all our earlier lives. At the slightest jerk our thought will flow down those old ruts. And notice when these jerks come. Usually at the precise moment when we might receive Grace. And if you were a devil would you not give the jerk just at these moments? I think that all Christians have found that he is v. active near the altar or on the eve of conversion: worldly anxieties, physical discomforts, lascivious fancies, doubt, are often poured in at such junctures ... But Grace is not frustrated. One gets more by pressing steadily on through these interruptions than on occasions when it all goes smoothly ...'
CS Lewis in Walter Hooper (Ed.), The Collected Letters of CS Lewis Vol III, p.93.
