“Mahamati, all phenomena are devoid of selfhood and are thus selfless. What I mean is that all things have their own individuality, which they do not share with another, as the principle taught by the Tathagata should be understood in the same fashion. For example, Mahamati, the being of a cow is not horse-nature, nor is the being of a horse cow-nature. Each of them is not without its own individuality. Each is as it is by its own nature.”
Excerpts from An Expostion on the Lankavatara Sutra
Venerable Xiao Pingshi
The Tathagata is referred to as “selfless” because it does not possess the nature of “selfhood” that sentient beings like to attach to themselves. The aggregates, sense fields, elements, and all dharmas that were directly or indirectly given rise to by the tathagatagarbha also do not possess a “selfhood” that is permanent and indestructible and are therefore said to be “selfless.” Thus, the notion that all dharmas are selfless is founded on the fact that they do not have the permanent nature of “selfhood.”
Of all the phenomena in the mundane world, dharmas have their own individuality. Each is as it is by its own nature, but due to the constant changing of all dharmas, which rely on conditions, decay, and eventually become extinct, they are said to be selfless.
The doctrine of selflessness found in the One-and-Only Vehicle of Bodhi, as well as “the selflessness of all phenomena” set forth by the Buddha must encompass both the aforementioned selflessness of all phenomena such as the aggregates, sense-fields, elements, and so forth and the aforementioned selflessness of the tathagatagarbha, due to the fact that both those phenomena and the tathagatagarbha are devoid of “the nature of the selfhood.” Thus, when we examine the relationship between the Tathagata and the five aggregates, we need to correctly delineate how the two can be different from each other and not different from each other at the same time.
Suppose that the Tathagata is not different from the five aggregates. As the five aggregates are impermanent dharmas, the Tathagata should also be an impermanent dharma and thus would also ultimately become extinct, just like the five aggregates. However, we know that the Tathagata is permanent, solid, and imperishable. Hence, it cannot be the same as the five aggregates, which will be eradicated. We cannot state, though, that the Tathagata is different from the five aggregates.
If the five aggregates differ from the Tathagata, then the Tathagata cannot abide in the bodies of the three realms (all beings have bodies) and will differ from the five aggregates in the three realms. Then the Tathagata entity self has nothing to do with the five aggregates’ bodies. If that is the case, the Tathagata will not be able to manifest together with the five aggregates in the mundane world or heavenly realms to benefit sentient beings by helping them accomplish karmic deeds, including Buddhist learning and cultivation and realization of the expedient paramitas. Thus, all efforts will become empty, meaningless, and unachievable.
As mentioned above, the Tathagata is neither different nor not different from the five aggregates. Neither can it be said that the five aggregates are the Tathagata, nor that the five aggregates are not the Tathagata.
An Exposition on the Lankavatara Sutra, Vol. 8, p.61 - 66