Tatiyanibbānapaṭisaṁyuttasutta: Why is Nibbana referred to as the 'unborn'?

> “There is, monks, an unborn, unbecome, unmade, unconditioned. If, > monks there were not that unborn, unbecome, unmade, unconditioned, you > could not know an escape here from the born, become, made, and > conditioned. But because there is an unborn, unbecome, unmade, > unconditioned, therefore you do know an escape from the born, become, > made, and conditioned.” ~ Ud 8.3 In contemporary discussions—particularly outside of Buddhist contexts, this passage is sometimes interpreted in a theistic or metaphysical sense, as pointing to an eternal, uncreated reality or an absolute ground of being that exists independently and “allows” for liberation.From this perspective, the statement “if there were not that unborn…” is read as implying a foundational ontological ground upon which conditioned phenomena depend. Within a Buddhist doctrinal framework, however, Nibbāna is often said to be neither a self nor a substance, and Buddhism explicitly rejects a creator God and eternal metaphysical essences. - Within early Buddhist doctrine, why is Nibbāna described using terms such as “unborn” and “unconditioned,” rather than simply as the cessation of suffering or defilements? - How should the conditional phrasing “If there were not that unborn…” be understood without reifying Nibbāna into an eternal substance or theistic absolute? - How do traditional Buddhist commentaries address or guard against eternalist or theistic readings of this passage?