There is a distinction between ‘Religious Zen’ and ‘Pure Zen’.
Religious Zen, is that of the Mahayana canon and speaks to the Bodhisattva path of Buddhahood. The Zen of Japan is certainly towards this view, however, the Ch’an of the old Zen masters tends to be on Pure Zen.
Pure Zen, is the absolute nature of Zen without the religious overtones and aspirations.
There is no Zen Bible, never was and never will be. There is the Mahayana Canon, that are a loose collection of writings speaking to the Bodhisattva Path, however, there is no specific practice called Zen in them.
One can know Pure Zen without embracing the Bodhisattva path, the Bodhisattva Path can be embraced without knowing Zen at all.
Zen Buddhism is the marriage of the Zen insight and the Bodhisattva Path, in creating a religious view and aspiration, and becomes its own thing. Those that reside in Pure Zen in where wisdom and knowledge flow, need not at all be a disciple of the Buddha or the Mahayana.