The concept of self in the Mahayana Parinirvana Sutra (hereafter MPS) is much different that in some traditions of Theravada Buddhism. For one thing the self is transcendent. On the other hand, for Theravada Buddhism the ‘being’ is the Five Aggregates.
The MPS understands that as beings we are innately transcendent—the most fundamental part of us will not die, in other words. The transcendent is really our true self which is also Buddha-nature. All beings possess it but unfortunately this nature is covered over by innumerable defilements. If we truly wish enlightement we have to remove the defilements which make our Buddha-nature seem absent and unattained.
We can see the basis for the MPS in passages like this in the Pali canon.
“Wherefore, monks, whatever is material shape, past, future or present, internal ... thinking of all this material shape as ‘This is not mine, this I am not, this is not my self,’ he should see it thus as it really is by means of perfect wisdom. Whatever is feeling ... whatever is perception ... whatever are the habitual tendencies ... whatever is consciousness, past, future or present, internal ... thinking of all this consciousness as ‘This is not mine, this am I not, this is not my self,’ he should see it thus as it really is by means of perfect wisdom. Seeing it thus, monks, the instructed disciple of the pure ones turns away from material shape, he turns away from feeling, turns away from perception, turns away from the habitual tendencies, turns away from consciousness; turning away he is detached; by his detachment he is freed; in freedom there is the knowledge that he is freed and he comprehends: Destroyed is birth, brought to a close the Brahma-faring, done is what was to be done, there is no more being such or so" (M. iii. 20).
What is innately free, namely, the transcendent self, is bound up with the Five Aggregates of form, feeling, perception habitual tendencies and consciousness. The Buddha teaches that our transcendent nature can reject each aggregate thus actualizing its nature and becoming independent. It is the Buddhist version of the via negativa. What is, therefore, detached becomes free of the five aggregates which are subject to death.
In some traditions of Theravada Buddhism, transcendence doesn’t appear to be evident—in fact, it seems to be denied. Nirvana occurs when the ‘being’ made up of the Five Aggregates has gone out since there is nothing behind or beyond the aggregates. In this respect, the being or self is identical with the five aggregates. Nirvana, in other words, is not like a flame that has gone out but results when the aggregated being has gone out. But this makes nirvana little more than mystical death which seems to fit well within the category of annihilationism (P., ucchedavada) which the Buddha was dead-set against.
This form of Theravada Buddhism is generally what Western Buddhists believe in who have contempt for the idea of self and anything in the Buddhist canon supportive of transcendence. Regrettably, such a grasp of Buddhism can be summed up with a few lines from Wallace Stevens’ poem, Sunday Morning. "Death is the mother of beauty; hence from her, / Alone, shall come fulfillment to our dreams / And our desires."