The idea of emptiness is really about putting an end to representational thinking—it is not some kind of Buddhist essence. In this regard, emptiness can never be turned into a doctrine because it is, itself, inane.
It is important to understand that in representational thinking nothing is sacred because it is empty and not real. What we can give thought to—even the Buddha Mind—is never other than empty, insubstantial, and unreal. It is like thinking of a bar of gold as if this head-image of ours were actual gold.
The action of representational thinking is where ordinary consciousness as subject stands over the concept or mental image as object. In the case of Zen Buddhism, the thing to be realized, namely, the One Mind, is represented by a concept or mental image and subsequently reified. This is representational thinking. We are in a delusional state inasmuch as we continually treat the One Mind representation as real. The task of a Zen master it to wake us up from our sleep of representational thinking.
The opposition and the confusion we experience in Zen is always between representational thinking and the object it is trying to represent but cannot be represented. By example, there is a split between the concept-representation of Buddha Mind and the real Buddha Mind.
Zen Buddhism is trying to stop representational thinking which the Zen adept is habituated to. This explains the oddball behavior of the Zen masters. The minute the Roshi sees us representing, wham!! he nails us. The One Mind or Buddha Mind cannot be represented, imagined, or conceived. Period. It only becomes possible to overcome representational thinking when it has stopped all at once—suddenly (hence the idea of “sudden awakening”). In that moment occurs the Mind to Mind transmission.