I'm in the middle of a work/vacation and, when I'm not working, I'm working my way through several books I've been wanting to get to. One is The Book of Mu. I haven't finished it yet but it's a compiled volume of commentaries on the koan Mu. It's a great book. I can tell you just in reading the first 1/3 I would recommend it. It has a few things about it that can be frustrating—lack of diacritical marks for Pinyin-but I'll save that for later.
It has caused me to think about an issue that I have found frustrating in Zen in the US: its sometimes close association with Unitarian Universalism (UU). In some ways this issue is academic and pointless. Who cares? Well, I do. Others care and, I think it might matter to Zen. Essentially, I suggest that it is possible to be Buddhist and integrate that into a UU framework, i.e. Zen-->UU. However, I don't think it is possible to go the other way (UU-->Zen) if you don't leave UU behind. If you don't, there are some significant syncretic problems you'll have (not that Buddhism isn't one enormous syncretic problem), and you're going to have to figure out how get beyond ego and self-interest. You may also piss off a lot of communities who are either "Buddhist by birth" or new converts to Zen. As to the last point, simply, UU can come off as cultural colonialism. I'm not going to discuss that one problem and UU because (1) I'm not UU and (2) UU has that problem with more than Zen and Buddhism generally. I can point you to many colleagues both UU and not who can speak about this with greater eloquence than I can. Trust me though, UU isn't a bridge builder when it picks and chooses from other cultures randomly and without a coherent theology.
I came to this conclusion about what way you move in Zen essentially reading The Book of Mu and through my own personal experience. The best way to describe it and perhaps to also do nothing more than confuse it is to use an analogy.
Learning to Drive a Car - Zen
Learning to drive a car Zen style is simple (sort of). Let's assume you want to learn to drive a car to get from A to B. (Give me some leeway here if you're a Zen practitioner. The analogy doesn't really hold in a Zen context. But assume for argument's sake there is getting from A to B as two different places.) So, you need to figure out how to get there and know nothing about doing it. A Zen driving school looks very similar to those in the US. You have to wait a bit until you're a certain age. At that age, you have a teacher and are given basic instruction on the operation of the vehicle and the traffic rules. You practice with a teacher under a set of rules and forms, e.g. drive in the right lane, stopping distance, use of signals, changing a tire, merging, etc. At first, they aren't likely intuitive but you work at them and eventually take a test. If you pass the test, ok. If not, keep practicing.
Learning to Drive a Car - UU
Learning to drive a car UU style. You want to get to A to B. You want to use a car to do it. You know you aren't happy at A but feel like B will be better. You find others who feel similarly about A and also want to get to B. Someone has started a car and left it running. It's a historically important car and has been an influential car but, you don't know that because no one is there. You and your friends hop in. You are the one wanting to get from A to B so you are driving. Your friends are simply there to help and to debate next steps and come to consensus when problems arise. As you're driving you encounter problems along the way both in the operation of the car and in getting along with the other cars on the road. You may see things that work with others and pick and choose along the way in furtherance of your goal of getting from A to B. For example, you see the Zen driver using his signals to indicate that he wants to pass or merge. You ask him about it and he is happy to show you how he uses signals. You take the signal technique and drive off into traffic paying no mind to the whole process and understanding of driving but only with a tool. Eventually, probably with injury to yourself and others, you'll get to B. At that point, you'll probably realize you don't want to be at B anyway and will head off for C.
Obviously, I don't think the UU approach to learning to drive works. There is no theory and, without theory, no understanding nor technique. Once you learn to drive a car you realize that driving a car isn't about driving a car but is simply an understanding and skill with limitless application. Thus, I think if you learn to drive Zen style, it's no problem to drive with UUs (just use caution!). If you learn driving UU style, it will cause a problem to bring that into a Zen school and, if you stop to really learn how to use signals and everything that the Zen driver teaches you while in your UU car, I'm pretty convinced you'll join the Zen school.
UU seems to be a mental road. Now, I certainly haven't cut off my mental road and gotten to the heart of the matter. I do know though that for Zen, it's about cutting off the mental road. Staying UU, seems to me to stay committed to the mental road without a technique.
“The theory of our modern technic shows that nothing is as practical as theory.” - J. Oppenheimer