from Lewis' letter to Owen Barfield, June 28, 1936
"I wish I could Christianise the Summa[something Lewis wrote to Barfield in their long discussion they called 'the Great War'] for you - but I dunno, I dunno! When a truth has ceased to be a mistress for pleasure and become a wife for fruit it is almost unnatural to go back to the dialectic ardours of the wooing. There may come a moment - one of those recoveries of virginity, or to speak more suitably to the subject, one of those Nth deaths, and then I'll try."
Lewis may well be joking here with the image of mistress vs wife, but it sounds reversed to me. In the accounts Lewis gives of his conversion, it seems as though it is the truth which is the wooer, and his will the wooed, rather than this way around.
But I guess, besides a possible joke, Lewis seems to be expressing a sense of spiritual fatigue, a sense that he needs to be revived or renewed before he can attempt this task. (Which he perhaps never did, at least if so it was never published).