As I understand it, the version with “I” was an already-existing phrase of the annihilationists of the Buddha’s time, who conceived of a self that would be annihilated at some future time (either automatically at death or through certain practices that would lead to annihilation of the self).
The Buddha, as he so often did, borrowed this well-known phrasing but changed the first-person “I” to the third-person “It”, cleverly stripping away the notion of a self from the phrase and bringing it more in line with the teaching on anattā. It must have been pretty effective, as it’s described as leading a practitioner right up to the verge of awakening (see AN 7.55).
You might find this note by Bhikkhu Bodhi interesting (from SN 22.55, note 75 (pp. 1060-63)):
The formula for resolution recommended by the Buddha occurs in the suttas in two versions, one used by the annihilationists, the other the Buddha’s adaptation of this; as the two versions differ only with respect to two verb forms, they are sometimes confounded in the various recensions…
The annihilationist version— explicitly identified as ucchedadiṭṭhi at 22:81 and classed among wrong views at 22:152 and 24:4—reads: no c’ assaṃ no ca me siyā, na bhavissāmi na me bhavissatti. At AN V 63,28-64,2, the Buddha describes this creed as the highest of outside speculative views (etadaggaṃ bāhirakānaṃ diṭṭhigatānaṃ), the reason being that one who accepts such a view will not be attracted to existence nor averse to the cessation of existence. It is problematic how the optative clause in the annihilationist version should be interpreted; perhaps it can be read as an assertion that personal existence, along with its experienced world, is utterly fortuitous (“I might not have been and it might not have been mine”). The clause in the future tense clearly asserts that personal existence and its world will terminate at death.
The Buddha transformed this formula into a theme for contemplation consonant with his own teaching by replacing the first person verbs with their third person counterparts: No c’ assa no ca me siyā, na bhavissati na me bhavissati. The change of person shifts the stress from the view of self implicit in the annihilationist version (“I will be annihilated”) to an impersonal perspective that harmonizes with the anatta doctrine. In the present sutta, resolving (adhimuccamāno) on the formula is said to culminate in the destruction of the five lower fetters, that is, in the stage of nonreturning (anāgāmitā). Elsewhere the formula includes a rider, yad atthi yaṃ bhūtaṃ taṃ pajahāmi, “what exists, what has come to be, that I am abandoning.” Contemplation of this is said to lead to equanimity. At MN II 264,29-265,20, practice guided by the full formula, with the rider, culminates in rebirth in the base of neither-perception-nor-non-perception (if the meditator clings to the equanimity) or in Nibbāna (if there is no clinging to the equanimity). At AN IV 70-74, resolution guided by the formula, again with the rider, leads to one of the five levels of nonreturning or to arahantship. At Ud 78,2-3 the shorter formula is applied to mindfulness of the body; one who dwells thus gradually crosses attachment, i.e., wins arahantship.
It may be significant that in the Nikāyas the precise meaning of the formula is never explicated, which suggests it may have functioned as an open-ended guide to reflection to be filled in by the meditator through personal intuition. As to the actual word meaning, the commentaries take the opening particle c’ to represent ce, “if”, glossed sace by Spk and yadi by Spk-pṭ. On this basis they interpret each part of the formula as a conditional. Spk explains the formula in the present sutta on the basis of the questionable reading c’ assaṃ, though its second alternative conforms to the superior reading c’ assa. I translate here from Spk very literally, rendering the lemma in the way favoured by the explanation: “If I were not, it would not be for me: If I were not (sace ahaṃ na bhaveyyaṃ), neither would there by my belongings (mama parikkhāro). Or else: If in my past there had not been kammic formation (kammābhi-saṅkhāro), now there would not be for me these five aggregates. I will not be, (and) it will not be for me: I will now so strive that there will not be any kammic formation of mine producing the aggregates in the future; when that is absent, there will be for me no future rebirth.”
I part with the commentaries on the meaning of c’, which I take to represent ca; the syntax of the phrase as a whole clearly requires this. The Skt parallels actually contain ca (e.g., at Uv 15:4, parallel to Ud 78). If we accept this reading, then (in the present sutta) the first “it” can be taken to refer to the personal five aggregates, the second to the world apprehended through the aggregates. For the worldling this dyad is misconstrued as the duality of self and world; for the noble disciple it is simply the duality of internal and external phenomena. On this basis I would interpret the formula thus: “The five aggregates can be terminated, and the world presented by them can be terminated. I will so strive that the five aggregates will be terminated, (and) so that the world presented by them will be terminated.” Alternatively, the first “it” might be taken to refer to craving, and the second to the five aggregates arisen through craving. In the additional rider, “what exists, what has come to be” denotes the presently existent set of five aggregates, which are being abandoned through the abandonment of the cause for their continued re-manifestation, namely, craving or desire-and-lust.
My understanding of this passage has been largely influenced by discussions with VĀT and Bhikkhu Ñāṇatusita. I am also indebted to Peter Skilling for information on the Skt and Tibetan versions of the formula.
