In what follows, the Buddha speaks of an inverted (upside-down or perverse) way of viewing things, and of the hidden nature of the True Self.
1) 'Again the Buddha spoke to Kashyapa, 'There are the so-called perversities ['upside-down' views or inverted views]. To think that what is suffering [duhkha] is happiness [sukha]: the Tathagata is impermanent and is extinguished in Nirvana just as fire is extinguished when its fuel is exhausted is [a cause of] great suffering. To think that the Tathagata is impermanent is a perversity. To think that suffering [duhkha] is happiness [sukha] : To attribute the view [drsti] of an [ordinary person] to the Tathagata's longevity is a perversity. To think that the three realms, which are suffering, are happiness, is a perversity. This is the first perversity.
'It is perverse to think that what is impermanent is permanent, and it is a perversity to think that what is permanent [nitya - constant, eternal] is impermanent. To think that the Tathagata's Nirvana is [the result of] cultivating utter emptiness - is a perversity. It is a perversity to think that a short life-span of a being will be lengthened by having [meditatively] cultivated utter emptiness since the result of that [meditative] cultivation is the quality [dharma] of permanent being. This is the second perversity.
'It is perverse to think that that which is not the Self is the Self, and it is perverse to think that that which is the Self is not the Self. One [i.e. a person, some commentator other than the Buddha] might say that all mundane [people] posit a Self and that it is a perversity to maintain that the Buddha taught that the Tathagata-garbha is the True Self, and [that therefore we need] to engage in the [meditative] cultivation of not-Self because of that: this is the third perversity.
[Note by Dr. Tony Page: most Buddhists who try to teach the Dharma only speak about the first statement - that we should not regard what is non-Self as Self - but remain perversely and stubbornly silent about the second injunction - that we should not regard the Self as non-Self. Is this not an indication and indictment of the way Buddhism is taught these days? The words 'biased' and 'unbalanced' perhaps spring to mind ...]
'It is perverse to think that that which is pure is impure and it is a perversity to think that that which is impure is pure. It is a perversity to say that the Tathagata, who permanently abides and whose body is not food-produced with fleshly organs, has a body that is food-produced and impure; that the Dharma and the Sangha are also extinguished upon Liberation. The foolish consider their impure bodies which lack the slightest element of purity and come to think that [they are] pure. This is the fourth perversity.' [Faxian version]
2) '[Kashyapa asked the Buddha,] 'Bhagavat [= Lord, 'Auspicious One'], is there or is there not a Self in the twenty-five levels of existence?'
The Buddha replied, ' "Self" signifies the Tathagata-garbha. All beings have the Buddha-dhatu - which signifies the Self - but although that which signifies the Self is unchanging [nitya - eternal, permanent] from the very beginning, it is concealed by a mass of countless afflictions [kleshas] and so beings are unable to get sight of it. Noble son, it is just like a poor woman who had a hidden treasure of much gold within her house, but there was nobody, large or small, in the house who knew of this. Then a certain stranger, skilled in expedient methods, spoke with that poor woman, "I will employ you now - you can come and work for me, clearing weeds." She replied, "I can't, but if you can show my son the hidden gold, then I will come straight away and do your work." He said to her, "I know certain methods; I'll show your son." She replied, "nobody in the house, large or small, even myself, knows [where the hidden gold is], so how can you know?" He said, "I am quite capable." She replied, "I want to see it - can you show it to me?" Then that man dug out the hidden gold from her house. When the woman saw it, she was delighted, and in amazement she revered that person. Noble son, the Buddha-dhatu [Buddha Principle, Buddha Essence, Buddha Nature] of beings is like that. All beings are unable to see it for, like that hidden treasure of which the poor woman was ignorant, they do not know this. I now reveal the Buddha-dhatu that all beings possess which is concealed by afflictions [kleshas - negative thoughts, feelings and actions] and cannot be seen, like the gold treasure that the poor woman did not know she had. The Tathagata will today reveal to beings the hidden treasure of the Enlightened Ones - the Buddha-dhatu. When beings see this, they will become joyful and take refuge in the Tathagata. The person who is skilled in expedient methods is the Tathagata; the poor woman is all beings beyond count; and the gold treasure is the Buddha-dhatu.' [Comment by Dr. Tony Page: note that the 'expedient means' referred to here is not the Buddha-dhatu itself - as some commentators would have us falsely believe - but merely the means or method of discovering that Buddha Principle within us].
3) '[As regards] the truth of the cessation of suffering: if one [meditatively] cultivates Emptiness, everything will be eliminated, and one will [conceptually] destroy the Buddha-dhatu. If one calls the cultivation of Emptiness the truth of cessation [of suffering], then do not the heterodox with their irrational [Emptiness] also attain the truth of cessation through their cultivation of Emptiness? You should know that everybody has the constantly present Tathagata-nature; when you eradicate the fetters, the afflictions [kleshas] will be eliminated forever and the constantly present Tathagata-nature will be manifested. When you have generated a single thought, you will attain wondrous results: you will have constant and blissful mastery called [the state of] Dharmesvara-raja [King of Dharmic Mastery]. This is deemed the cultivation of the truth of the cessation of suffering. Moreover, when you [meditatively] cultivate the Tathagata-nature and treat it as Emptiness and non-Self, you should know that you will be like a moth falling into a flame. What I term the truth of cessation [of suffering] is the Tathagata-nature, the reality of the Tathagata, the elimination of all innumerable afflictions. Why is that? Because of the Tathagata-nature; those who know that will know the truth of cessation on a level with the Tathagata. Anything other than this is not called cessation.' [Faxian version] [Comment by Dr. Tony Page: This is one of the most important passages in the entirety of the Nirvana Sutra: it proves once and for all that not only is it contrary to true Dharma to apply the notion of non-Self to the nirvanic realm (i.e., the Buddha Essence - the Buddha-nature), but that it is positively dangerous so to do. To regard the Buddha Essence as non-Self and empty in one's meditations is tantamount to committing self-immolation - a form of fiery spiritual suicide. The Buddha could scarcely have made the point more graphically than this].