Why does the Tathāgata have no fixed Dharma to speak?

Original text of the Diamond Sutra: 须菩提言。如我解佛所说义。无有定法。名阿耨多罗三藐三菩提。也无有定法。如来可说。何以故。如来所说法。皆不可取。不可说。非法。非非法。一切圣贤皆以无为法而有差别。

The explanation of this passage is as follows: Subhūti replied to the Buddha: According to my understanding of the meaning of what the Buddha taught, there is no fixed, unchanging dharma called anuttarā-samyak-saṃbodhi, and there is no substantially existent dharma called anuttarā-samyak-saṃbodhi. Why is this said? Because anuttarā-samyak-saṃbodhi is also called unsurpassed, complete, and perfect enlightenment, which means the accomplishment of the Buddha Way; and becoming a Buddha is not something innately existing or a fixed, unchanging dharma—it is achieved later through cultivation over three great asaṃkhyeya kalpas. Therefore it is also subject to arising and ceasing; it comes from nonexistence into existence. Hence it is not a fixed dharma, nor a substantially existent dharma.

Nor is there any fixed dharma that the Tathāgata can teach. Why is this said? Because the Tripitaka and twelve divisions of scriptures that the Tathāgata taught over forty-nine years in the Sahā world cannot all be grasped as substantially existent; indeed, all the dharmas the Tathāgata taught in the worlds of the ten directions cannot be grasped as substantially existent. Why can they not be grasped as substantially existent? Because all the dharmas the Buddha taught arose due to various causes and conditions; without causes and conditions, these dharmas would not exist, and the Buddha would not have taught any dharma. Even the great matter of the Buddha delivering sentient beings requires the ripening and completeness of causes and conditions, requiring sentient beings' merit, causes and conditions of good roots, and the aspiration for liberation, and so forth. Lacking even one cause or condition, the Buddha cannot deliver sentient beings. And the dharma taught to deliver sentient beings is determined according to causes and conditions, determined according to sentient beings' indriya, merit, and wisdom—there is no fixed dharma to be taught.

A fixed dharma means a dharma that is fixed and unchanging, originally existent, that does not turn with causes and conditions, does not vary with causes and conditions—a truly real, immutable dharma, where the same dharma is used for all sentient beings regardless, regardless of what faculties sentient beings possess, and regardless of what causes and conditions are present, the same dharma is used. Obviously, this is incorrect, unachievable, and unworkable; such a dharma does not exist. Dharmas produced by causes and conditions, dharmas not innately existent, are all not fixed dharmas. Therefore it is said that the Tathāgata, in delivering sentient beings, has no fixed dharma to teach.

Therefore the dharma taught by the Tathāgata cannot be said to be a substantially existent, immutable dharma; it is also a dharma of arising, ceasing, and change, coming from nonexistence into existence, existing and then becoming nonexistent, a raft to be abandoned upon reaching the other shore; it is also an empty dharma. Hence it is merely named "dharma"; in reality, dharmas have no self-nature, no self-substance to speak of, and therefore it is not-dharma. Yet it is also not entirely not-dharma, for after all there is still its illusory function; the provisional dharma can nevertheless be used provisionally and borrowed for use—sentient beings can use it to become Buddhas, and after becoming Buddhas, they then abandon it. Therefore the dharma taught by the Buddha is also not-not-dharma; it is not that it is not a dharma.

Since all the dharmas taught by the Tathāgata are not-dharmas, dharmas produced by causes and conditions, with no fixed dharma, then the dharmas the Tathāgata taught to sentient beings of different indriya according to different causes and conditions, when cultivated and studied by sentient beings, lead them to realize unconditioned dharmas of different levels, including the unconditioned of the Great, Middle, and Small Vehicles, and even the unconditioned dharmas within the same vehicle have differences. Thus sages and worthies of different levels and different distinctions are accomplished. All sages and worthies, because their good roots, merit, and causes and conditions differ, are distinguished by the unconditioned dharma they have realized.