If you are thinking, you can't understand Zen. Anything that can be written in a book, anything that can be said - all this is thinking . . . but if you read with a mind that has cut off all thinking, then Zen books, sutras and Bibles are all the truth. So is the barking of a dog or the crowing of a rooster. All things are teaching you at every moment, and these sounds are even better teaching than Zen books.