If you could keep just one witchcraft book, which would you pick?

I’d pick The Crooked Path by Kelden if I wanted a book centered on traditional witchcraft. It gives you a particular direction to explore rather than trying to be a guide to every kind of practice, so it makes more sense if that approach suits you.

For a reference shelf reduced to one book, I’d choose The Encyclopedia of 5,000 Spells by Judika Illes. A spell collection is handy for browsing and comparing ideas, though it’s less of a step-by-step guide to building one complete practice.

I wouldn’t look for a single book that covers everything. I’d keep the one that fits the way I actually want to practice, whether that means a focused tradition, practical exercises, or a reference book. A title that suits your path will be more useful than a supposedly universal pick.