You have asked what the Buddha-dhatu [Buddha Nature, Buddha Essence] is, so listen with sincerity, listen with sincerity, I shall analyse and elucidate it for your sake.
Nobly-born son, the Buddha-dhatu is termed “ultimate emptiness” [paramartha-sunyata], and ultimate emptiness is termed Awareness [jnana – gnosis]. So-called emptiness is neither viewed as emptiness nor as non-emptiness.
The wise perceive:
- Emptiness AND non-emptiness,
- The permanent AND the impermanent,
- Suffering AND bliss,
- Self AND non-Self.
- The empty is the totality of samsara and
- The non-empty is Great Nirvana [and so forth down to]
- Non-Self is samsara, and
- The Self is Great Nirvana.
To perceive the emptiness of everything and not to perceive non-emptiness is not termed the Middle Way [and so forth down to], to perceive the non-Self of everything, and not to perceive the Self is not termed the Middle Way.
The Middle Way is termed the Buddha-dhatu. For this reason, the Buddha-dhatu is eternal and unchanging.
Because beings are enveloped in ignorance, they are unable to perceive it. Sravakas and pratyekabuddhas [i.e. relatively high-level spiritual aspirants, but lower than full Buddhas] perceive the emptiness of everything, but do not perceive the non-emptiness [and so forth down to], they perceive the absence of self [i.e. non-Self] in all things, but do not perceive the Self.
For this reason, they do not attain the ultimate emptiness. Because they do not attain the supreme emptiness, they do not walk the Middle Way. Because they lack the Middle Way, they do not perceive the Buddha-dhatu.’
Source: The Mahaparinirvana Sutra http://www.nirvanasutra.net/stephenhodgetrans4.htm
So here, the Buddha says that to maintain a balanced approach to understanding, you’ve got to walk the middle way – having BOTH the understanding of:
- What things are empty vs what is not empty
- What things are of a transient nature and what things aren’t
- What things have the nature of suffering and what things don’t
- Those things which are not fit to be regarded as self and that which is fit to be regarded as Self
If you do have a balanced understanding of these things, then you will be walking the Middle Way – the balanced approach.
- Samsara – is empty because it is illusory, transient and nothing in samsara is worthy to be regarded as Self.
- Nirvana – is not empty because it has done away with illusion, done away with the transient and done away with suffering. So it is reality, it is eternal and it is the utmost happiness.
So see why it’s important to understand what these terms are applied to? A lot of Buddhists indiscriminately apply these terms to absolutely everything, without realizing that these terms are contingent and only applied in a very specific way. They say “Everything is impermanent, everything is suffering, everything has no self, everything is empty” – but the Buddha says that this is unbalanced, and so, is not the Middle Way.
So make sure you understand – the basics of vipassana meditation – anicca, dukkha, anatta – only apply to things that are transient/impermanent and therefore samsaric in nature.
Anything that does not have a transient nature must therefore be eternal (anything beyond time is akaliko – timeless). Anything that no longer has suffering must therefore be the ultimate happiness (Nibbanam paramam sukham). And when attachment to all that is non-self is abandoned, then there is the Self of Great Nirvana.