The term ‘Buddha Nature’ first appears in the Tathagatagarbha Sutra and in a number of subsequent sutras, most famously the Nirvana Sutra and thence, via the Lankavatara Sutra, into Zen, hence the most famous koan about whether or not a dog has Buddha Nature
The Tathagata Sutra is a really interesting sutra. It’s very short and it’s not discursive. It has an instruction, then eight similies for Buddha Nature.
The introduction was apparently added later. In it, the Buddha is giving a talk to a large number of named bodhisattvas. He performs a kind of conjuring trick, miraculously creating the appearance of a multitude of beautiful lotus flowers in the sky. Within each lotus flower, there’s a Buddha.
After the initial vision, the lotus flowers suddenly wither, giving off a foul stench.
The similes used are interesting too:
The first is honey in a cave or a tree surrounded by a swarm of bees;
The second is a kernel of wheat that has not had the husk removed;
The third is gold in a pit of waste;
The fourth is an unknown treasure underneath a poor person’s house;
The fifth is the core of a fruit which can then develop into a magnificent tree;
The sixth is a gold statue wrapped in filthy rags;
The seventh, which probably gives the sutra its name, is (and I’m quoting) ” an impoverished, vile and ugly woman, hated by others, who bears a king in her womb”;
The last one is a golden statue which has been in a foundry, so has a dark casing.
All of these similes refer to the kleshas. ‘Klesha’ literally means poison and in this context means a mental state that clouds the mind. There’s lots of them: ignorance,
self-centeredness, attachment, avoidance, and fear, and many others.
Klesha is often translated as ‘adventitious defilements’. This is typical of an elevated way of translating which, focusing on apparent accuracy of meaning, distances us from the emotional sense of the term translated. In a similar way, is-ness is often rendered as thusness, and we lose the sense of “well, it doesn’t (independently and separately) exist but it doesn’t not exist either, so what do we call it?”; a human sense, that you can imagine real people actually saying. This does seem to happen in translation quite a lot. For example, when Ernest Jones translated Freud he rendered ‘Ich’ (‘I’) as ‘Ego’, with predictable consequences.
Given the ubiquity of euphemism, my guess is that the pit of waste is really a pit of shit. The dirty robes/rags are probably something similar. Despite that, the emotion in these similes remains clear:
the angry swarm of bees protecting the honey is anger;
the kernel of wheat inside the husk that is unknown is ignorance,
the the pit of shit is disgust;
the treasure beneath the poor person’s house is ignorance again,
the core of the fruit, ignorance again;
the gold statue wrapped in filthy rags, disgust again;
the impoverished vile woman, disgust;
a golden statue wrapped within a dark casing, ignorance;
and the initial image that we have about these flowers giving off a foul stench is obviously disgust as well.
These are emotions that we generally don’t want to go anywhere near—just like we wouldn’t want to go near a pit of shit, we don’t want to go near our disgust, our anger and so on.
If we pay attention to the emotions which are invoked by these similes then I think we can understand how the Tathagata, far from being some quaint Chinese medieval device, is actually a very good description of Zazen.
When we’re sitting we’re aware of this kind of dynamic emptiness – this treasure – at our centre.We’re also aware of all our surrounding nonsense: our fluctuating thought babble, emotions, images and all the rest. All of which are just coming and going and which we can see doesn’t really exist. That’s where the introduction is helpful, because it is saying that these stinking lotus flowers, these kleshas don’t exist either, because they’re all taking place within the Buddha’s conjuring trick.
If you understand all of that, then it seems to me that the Tathagatagarbha is a very helpful and practical way of looking at our practice and our experience in Zazen.