大般涅槃經義記 2.196

2.196

上來第一當問正解，明斷無常故得為常。自下明佛證常故常。「諸佛所師所謂法」者，舉所證法。如來藏性成德所依，故名佛師。「是故如來恭敬供養」明能證行。是佛師故，如來敬養。佛本因中所修諸行，內順真性名為恭敬，熏真成德說為供養，以法常故諸佛亦常，證實成德法性緣起成佛報果，法性常故報佛亦常。

The above is the first part, providing the correct explanation addressing the question, clarifying that because he cuts off the impermanent, he is therefore permanent. From here down, it clarifies that because the Buddha realizes the permanent, he is permanent. 'That which all buddhas take as master is the so-called Dharma' cites the Dharma that is realized. The nature of the tathāgatagarbha is the basis for the perfection of virtues, and is therefore called the master of buddhas. 'Therefore the Tathāgata reveres and makes offerings to it' clarifies the practice of the one who realizes it. Because it is the master of buddhas, the Tathāgata reveres and makes offerings to it. Regarding the various practices cultivated by the Buddha in his original causal stage, inwardly according with the true nature is called reverence, and perfuming the true to accomplish virtue is spoken of as making offerings. Because the Dharma is permanent, all buddhas are also permanent: realizing the real and accomplishing virtue, the conditioned arising of dharmatā accomplishes the reward fruit of the Buddha; because dharmatā is permanent, the reward buddha is also permanent.