Zen can be thought of as a vehicle or somewhat like a device that is used to get us to Buddhism's enlightenment. This sounds simple, but there are a few ways this can go wrong. If we think of Zen as a vehicle like an SUV, we can drive it onto another road that has little or nothing to do with Buddhism's highway. It becomes more like a personal vehicle in that respect, fitting our special case desires and needs. Others may see Zen as a device or instrument like a hammer who use it to build an anti-religious, secular Zen being something close to agnosticism. It has limited aims only extending to sitting in meditation.
Getting to know Zen on its own terms requires a fair amount of study and work. It doesn't come easy when we take into consideration its founders who were all deeply steeped in Mahayana Buddhism. Zen was more of a literary genre, you might say, a unique way of presenting Mahayana Buddhism than anything resembling a particular sect. In fact, there is no indication in the history of Zen that it was ever a sect in the Western sense of the word, that is, a dissenting religious body. Unlike with Theravada Buddhism, Mahayana did not have a closed canon. It was still growing, in other words. Zen is a reflection of such growth you might say.
Zen used too much for our personal needs and ends, easily, becomes less than Zen such that we lose the scent for authentic Zen. The name remains; so do the robes and the temple; even zazen remains, but the heart of it is dying. Those who try to correct the modern view of Zen and for that matter, Buddhism, are looked upon with some disfavor. Nothing they say is understood; certainly not worth listening to. Zen becomes degenerate at some point. It breaks up into splinter groups each with varying interpretations and practices.
In my own example, Zen in the late 1950s and early 1960s was a cool, hip thing to study—great in conversations at some parties. Not too much was known about it. It was mysterious. If you were lucky and a good academic library was nearby you were in luck to learn more about Zen and Mahayana Buddhism. It never dawned on any of us at the time that Zen was something to help with depression; that doing lots of zazen was helpful for mental stress and anxiety. Zen was just a cool thing like Taoism. Chinese Zen masters were mysterious old guys that lived in a hut and blissed out on their satori. In some ways this idealistic, new vision was more on the mark than where Zen is heading these days. Back then, some of us wanted to take this odd vehicle to the end of the Buddhist highway.