Not an uncommon question for a beginner is what book about Zen should I read? Believe me, I have had to do some thinking about this. It is not that easy—what would I recommend? There are lots of books about Zen. I am familiar with many of them. But for the sincere beginner something special is needed than starting with a book of koans such as Zen Flesh, Zen Bones by Paul Reps, for example.
Nietzsche was right when he said: "He who would learn to fly one day must first learn to stand and walk and run and climb and dance; one cannot fly into flying." Unfortunately, almost all beginners try to fly into flying. It is difficult to get them to understand that a book of koans is almost useless without sufficient grounding in Buddhism and how Zen fits in with it. The same goes with even doing seated meditation.
For the most part, Westerners have only been guessing about Zen Buddhism. Some of the guesses are refined and very good; others are almost laughable. Ironically, Zen doesn't go out of its way to be difficult. In almost every Zen sermon or letter to a student by a Zen master, what Zen is actually pointing to is to be found, but only if beforehand we understand the context of Buddhism and Zen Buddhism, this context being mysticism. If we fail to comprehend the importance of this context, harking back to Nietzsche's words, we are only standing—not even walking. Flight at this point is impossible.
Western culture is still not quite capable of understanding Zen or even Buddhism. When in the 19th century Buddhism was disclosed to the West, many thought it to be a creed of reason without God or a soul, without a heaven or a hell, without miracles, even lacking anything remotely transcendent. But the West was all wrong. Buddhism turned out to be a unique religion much broader than the Judeo-Christian concept insofar as there was no need of relationship between man and a personal God. Buddhism recognizes that all beings have the potential to awaken to the transcendent. However, the transcendent is hidden and undeveloped within them. They can't see it because of their unbroken clinging to adventitious phenomena.
Awakening to the transcendent, which is at the heart of Zen Buddhism, should be recognized in the West as mysticism. But the Buddhist notion of mysticism, including Zen, is not concerned with sorcery, black magic, divination, or metaphysics. It is deeply involved with penetrating through the veil of phenomena; seeing on the other side of this veil the very stuff our thoughts and the world are composed of. In this sense, mysticism can be further described as the apprehension of ultimate reality, a reality, however, empty of all conditioned things and, itself, unconditioned.
If I had a class such as Zen Buddhism 101 much of my lecture would come from Heinrich Dumoulin's book, A History of Zen Buddhism (1963). I wouldn't follow it to the letter but certain chapters I would cover more thoroughly. Also, I would supplement Dumoulin's work with Hajime Nakmura's wonderful book, Ways of Thinking of Eastern Peoples: India-China-Tibet-Japan (1971) especially his sections on China and Japan.