Thatness (tathata), Emptiness (shunyata), Reality-limit (bhuta-koti), Nirvana, Dharma Substrata (dharmadhatu) are like the multiple bodies made of spirit (manomaya-kaya)—these are taught as being synonymous (prayaya). — Lankavatara Sagathakam
This is quite a statement. It should be carefully noted that all these terms have positive implications as does even the term "emptiness". But for the unwary Zen student, whose mind is beclouded with his suppositions of what Zen is supposed to be, this means almost nothing. This pericope from the Lankavatara Sutra means, however, more than any careless Zen student can imagine.
It is of great importance if we are going to reach the other shore. We can't remain on this shore, running along side of it, fooling ourselves, imagining that we have reached the other shore if we stand with our backs towards the wide ocean of samsara we have to cross.
Thatness, Emptiness...Nirvana, Dharma Substrata are just other names of that divine world that lies across the wide ocean of samsara. They have no reference to this world—the world many Zennists still hold dear, hoping to find enlightenment in the external formalisms of Zen such as zazen (i.e., sitting Zen).
This divine world—yonder shore—is really a spiritual body that lies within us which is naturally unyoked from the mortal body. About this body, the Buddha says the following in the Samaññaphala Sutta of the Digha-Nikaya:
"From this body he creates another body, endowed with form, made of the mind, complete in all its parts, not inferior in its faculties. Just as if a man were to draw a reed from its sheath. The thought would occur to him: 'This is the sheath, this is the reed. The sheath is one thing, the reed another, but the reed has been drawn out from the sheath.' Or as if a man were to draw a sword from its scabbard. The thought would occur to him: 'This is the sword, this is the scabbard. The sword is one thing, the scabbard another, but the sword has been drawn out from the scabbard.' Or as if a man were to pull a snake out from its slough. The thought would occur to him: 'This is the snake, this is the slough. The snake is one thing, the slough another, but the snake has been pulled out from the slough.' In the same way—with his mind thus concentrated, purified, and bright, unblemished, free from defects, pliant, malleable, steady, and attained to imperturbability, the monk directs and inclines it to creating a mind-made body (manomaya-kaya). From this body he creates another body, endowed with form, made of the mind, complete in all its parts, not inferior in its faculties."
What is striking about the above passage is that we see direct evidence of a transcendent body in scripture that is free from the Five Aggregates. In this particular passage, the Buddha is teaching the acquisition of this supra body after clearly distinguishing the carnal body made up of the four great elements, born of mother and father, subsisting on food, etc., upon which consciousness is bound in dependence (cp. D.i.76).
This spiritual body lies, metaphorically speaking, on the other shore which is only found when we depart from the carnal body consisting of the Five Aggregates (form, sensation, thought, experience, and consciousness). To begin to access this supra body we have to peel back the layers mind constructions that make up our subjecthood to which we are attached. We will eventually reach a limit where both subject and object are eclipsed (i.e., the internal and external world). It is from this limit (bhuta-koti) that we disengage from our carnal body and the data of the natural world which streams through it. It is only here that real emancipation is to be found.