Dogen on Samsara and Nirvana

Not only that, you must fully understand that ‘birth and death’ is nirvana: there has never been any talk of a nirvana outside of birth and death. Moreover, even though you may erroneously reckon that there is a Buddha Wisdom that is separate from birth and death because you have worked it out that the mind permanently abides apart from the body, this ‘mind’ of yours—which understands, and works matters out, and perceives things, and knows what they are—is still something that arises and disappears, and is in no way ‘everabiding’. Surely, this ‘mind’ of yours is something completely transitory!
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"In addition, should you suddenly get the notion that eradicating birth and death is what the Dharma is really about, it would lead you to sullying the Precept against despising the Buddha Dharma. Do watch out for this!
Shobogenzo, Bendowa, Rev. Hubert Nearman, O.B.C