大般涅槃經義記 2.87

2.87

第三法力得果之中，初問「云何作船師」者，問化他德。下答如來得涅槃船，故能濟渡，為大船師。「云何捨生死如蛇脫皮」問自利德，下答如來滅而常存，故得如蛇脫皮不死。分別有二：一據修入辨，捨妄契實，如蛇不死；二就息化歸真以釋，滅應歸真，如蛇不死。

In the third part, on the power of the Dharma to attain the fruit, the initial question, "How does one become a helmsman?" asks about the virtue of transforming others. Below, the answer states that the Tathāgata attains the raft of nirvāṇa and is therefore able to ferry across, being a great helmsman. "How does one cast off birth-and-death like a snake shedding its skin?" asks about the virtue of self-benefit. Below, the answer states that the Tathāgata extinguishes yet constantly abides, and thus is like a snake shedding its skin without dying. The differentiation is twofold: first, explained in terms of cultivation and entry, shedding delusion and tallying with reality, like a snake not dying; second, interpreted in terms of ceasing transformation and returning to the real, extinguishing the manifest response and returning to reality, like a snake not dying.