When Yung-chia says that the Dharma body of all Buddhas enters his nature, he is correct, because his nature is in no way different from the nature of all Buddhas. But if you were to say, "I am identical with the Dharma body of all Buddhas, " or, "All the Dharma bodies of all Buddhas are within me, " then you are mistaken. To say that you are never apart from the Dharma body of all the Buddhas is correct, but you cannot claim that you are the Dharma body of all the Buddhas.
Your nature, my nature, and the nature of the Buddhas are one ─ combined and never apart ─ so it is impossible to point to something in yourself and say, "This is my own nature, " and point elsewhere and say, "That is the nature of the Buddhas." You cannot separate them.
Mist and ice may be in different physical states, but they are still water. The water in milk is the same as the water in tea, and it is the same as the water in my body and in the ground outside. It can manifest in infinite ways, amounts, and places, but its basic nature is water. In the same way, the Tathagata's nature is the same as your nature.
Even though we speak of unlimited Dharma gates, innumerable Buddhas, and infinite manifestations of Buddha-nature, if in a single moment you realize your true nature, then you come face to face with all the Tathagatas and Buddhas. It means that you are not separate from them.