Why are the mark of self, the mark of others, the mark of sentient beings, and the mark of a life span all no-marks?

Original text:若当来世。后五百岁。其有众生。得闻是经。信解受持。是人则为第一希有。何以故。此人无我相。无人相。无众生相。无寿者相。所以者何。我相即是非相。人相众生相寿者相即是非相。何以故。离一切诸相。则名诸佛。

Explanation: If in the latter five-hundred-year period before the Dharma of the Buddha is destroyed in a future age, there are still sentient beings who are able to hear this Diamond Sutra, and who possess pure faith, correctly understand the vajra mind, and receive and uphold the Diamond Sutra, such a person is the rarest of all. Why is this person the rarest of all? Because this person no longer has the mark of self, the mark of a person, the mark of sentient beings, or the mark of a life span. Why does this person have no four marks? Because the mark of self is not a truly existent mark, the mark of a person is not a truly existent mark, the mark of sentient beings is not a truly existent mark, and the mark of a life span is not a truly existent mark. Why is this said? Because every Buddha is free from all marks, and only one who is free from all marks is called a Buddha.

In the latter five hundred years when the Buddha's Dharma is about to be destroyed, the world will be even more turbid and evil, sentient beings' afflictions will be heavier, and their wholesome roots will be even scarcer. If at such a time there are still sentient beings who can hear the Diamond Sutra, their wholesome roots and merit must be very deep. Having heard it, they believe and accept it deeply, realize and understand the vajra mind, and protect and transmit the Diamond Sutra. Such a person is one of extremely deep wholesome roots, a very rare, long-cultivating bodhisattva, no longer an ordinary person. After realizing the vajra mind, they clearly understand the principle of the emptiness of the five aggregates, and in their mind there is no longer the mark of self, the mark of a person, the mark of sentient beings, or the mark of a life span. These marks exist dependent upon the five aggregates; once the five aggregates are seen as empty, the four marks vanish, the virtuous marks manifest, and such a person is a rare sage.

Why can the four marks disappear? Because the four marks are not truly existent marks in the first place; they are illusory marks conjured by the vajra mind, and therefore are of a nature of arising and ceasing, empty, and unattainable. If they were truly existent marks, they could not be emptied, and no matter how hard one strives, one could not make these marks disappear. After realizing the vajra mind, when encountering conditions and facing objects, one observes in the present moment that the mark of self arises from the vajra mind, the mark of a person arises from the vajra mind, the mark of sentient beings arises from the vajra mind, and the mark of a life span also arises from the vajra mind. In this way, the four marks are gradually extinguished completely, and the wisdom of the mark of emptiness becomes ever deeper. Then one gradually empties the other dharma-marks as well; when all dharma-marks are completely emptied, Buddhahood is accomplished.

Therefore the Buddha said: "Free from all marks is called all Buddhas." Here "all Buddhas" has two meanings: one refers to the Nirmāṇakāya Buddha possessing a body of the five aggregates, and the other refers to the Dharmakāya Buddha (dharma-kāya-buddha). The Dharmakāya Buddha itself has been free from all marks since beginningless kalpas, empty without a single mark, formless and markless, without the marks of form, sound, smell, taste, touch, or dharmas; the true countenance cannot be seen by means of the eye, ear, nose, tongue, body, or mind. At this time, the Nirmāṇakāya Buddha is also free from all marks, empties all marks, and does not cling to any mark. When the Nirmāṇakāya Buddha and the Dharmakāya Buddha are identical in mind-nature, equally pure and non-active, that is the Buddhas of perfect merit and virtue.