The first patriarch of Zen, Bodhidharma, is not actually a patriarch of Zen, instead, he is the patriarch of the Lankavatara Sutra tradition, sometime refered to as the Lanka School or Lanka Realization. The preeminence of the Lankavatara Sutra was eventually, and oddly, replaced by the Vajracchedika Sutra (Diamond-cutter Sutra).
Nevertheless, Zen retained almost entirely its allegiance to the Lankavatara Sutra by embracing the notion of Mind (with a capital ‘M’ denoting that it is absolute); in particular pure Mind devoid of appearance (nirabhasa ).
Also, from the Lankavatara Sutra, Zen understood that this pristine Mind is set in contrast to sva-citta-drisya-matra, that is, mind, itself, in the mode of appearance. There are many more facets of the Lankavatara Sutra that Zen embraces.
According to the Lankavatara Sutra, the only way to apprehend Mind is by a non-theoretical path. Zen, to be sure, subscribes to this in a very big way. It is the main feature of Zen unlike other Buddhist sects which engage in theoretics.
Because of its distaste for theoretics, it is easy to see why Zen is regarded as the mystical wing of Buddhism. Its goal concerns catching a glimpse of pure Mind—if only for a second.
It hardly needs further comment that this glimpse is extraordinarly difficult to accomplish. Without dragging in my own experiences, it is no less extraordinary than having the Buddha appear in one’s room. After such an experiece—Sutras like the Lankavatara take on a new meaning. To be sure, one is also awed by the mystical depth of the Zen masters of old.
On the same thread, the great awakening comes when the totality of our mental life, which is only an appearance, and the external world (bahyartha), which also is only an appearance, are both fully transcended by seeing pure Mind sufficiently. Indeed, Mind, itself, is neither subjective nor objective. It is, in fact, our very self as it stands (svapratyatmagati) according to the Lankavatara Sutra. This state (gati), in addtion, puts us elsewhere preceptually than in the body or with the world. To be sure, it is a unique experience. We are at once disembodied—and not of this world or any other.