_The nature of the Absolute is void and yet not void. How so? The marvellous "substance" of the Absolute, having neither form nor shape, is therefore undiscoverable; hence it is void. Nevertheless, that immaterial, formless "substance" contains functions as numerous as the sands of the Ganges, functions which respond unfailingly to circumstances, so it is also described as not void.16
By focusing on this idea of unity in an Absolute, we also interact with our own perception of time. Since it is important that the mind not dwell on anything, naturally enough this applies to time as well as space.
_If you want to understand the non-dwelling mind very clearly, while you are actually sitting in meditation, you must be cognizant only of the mind. . . . Whatever is past is past, so do not sit in judgment upon it; for when minding about the past ceases of itself, it can be said that there is no longer any past. Whatever is in the future is not here yet, so do not direct your hopes and longings towards it; for, when minding about the future ceases of itself, it can be said that there is no future. Whatever is present is now at hand; just be conscious of your non-attachment to everything--non-attachment in the sense of not allowing any love or aversion for anything to enter your mind; for, when minding the present ceases of itself, we may say that there is no present.17
He has taken the idea of the "now" to an interesting new dimension. By cutting off thoughts of past and future, you not only save yourself mental anguish, you also no longer need distinguish the idea of the "present" . . . and you have just eliminated a major aspect of attachment.
Huai-hai is not blind to the difficulty of such rigorous mind control, and he offers some of the first practical advice from a Ch'an master for controlling the mind. Not surprisingly, it is an admonition to stop trying so hard, to just focus on goals rather than forcing the mind's behavior. For example, if you are meditating and your mind wants to meander and look for something to dwell on, what should you do?
_Should your mind wander away, do not follow it, whereupon your wandering mind will stop wandering of its own accord. Should your mind desire to linger somewhere, do not follow it and do not dwell there, whereupon your mind's questing for a dwelling place will cease of its own accord. Thereby, you will come to possess a non-dwelling mind--a mind which remains in the state of non-dwelling. If you are fully aware in yourself of a non-dwelling mind, you will discover that there is just the fact of dwelling, with nothing to dwell upon or not to dwell upon. This full awareness in yourself of a mind dwelling upon nothing is known as having a clear perception of your own mind or, in other words, as having a clear perception of your own nature.18