Ṭhānissaro Bhikkhu, also known as Ajaan Geoff (born Geoffrey DeGraff, 1949), is an American Theravada Buddhist monk of the Dhammayut Order (Dhammayutika Nikaya), Thai forest kammatthana tradition. He is currently the abbot of Metta Forest Monastery in San Diego County. Ṭhānissaro Bhikkhu is a translator of the Pāli Canon as well as more modern Buddhist works and the author of many articles and books on Dhamma.
These dhamma texts can be somewhat repetitive if you're already thoroughly acquainted with the basic concepts of the tradition, though this one has the benefit of being nice and short. The selections from the Canon used to elucidate the author's points are salient and particularly beautiful, though there is still plenty of catuṣkoṭi logical wrangling.
In this case, the main thrust of the work is an elaboration upon the various analogies in the Pali Canon of the mind as a flame which needs clinging to continue burning, and the highly attained mind as fire extinguished and thus 'unbound'. Fire, according to Vedic physics, still exists latently, is not annihilated, but has simply gone 'out' [nibbuto, the root for nibanna] of conditioned-ness into omnipresent-ness, with a few different necessary phenomenological stages along the way.
There is a very subtle philosophical understanding that the Buddha tries to impart on how exactly this is possible. The author repeatedly cites verses to emphasise this understanding. Namely, that to the unbound mind the question of existence and non-existence is immaterial, and thus it cannot be understood in these terms, but rather through a framework of release and unbinding, which the author considers one of the most potent formulations of nibbana. When he is unbound, Agni goes ‘out’, but he is not destroyed; rather, he lets go of his fuel, becomes calm, and is freed from confinement. Similarly, the highly attained mind is no longer attached to the aggregates that compose sensual experience, ending the cycle of grasping that feeds the flame. ("...it is only stress that I describe, and the stopping of stress.")
The plane of linguistic possibility that applies to such a mind has now altered; questions of existence simply no longer apply, even Indra can only pay homage from afar to this eminently untethered superlative man (AN 11:10). Worth noting here is that sensibility is not merely physical nervous sense, but the entire aggregate of experience conditioned by space and time, including mental formation, feeling, and all the innate structures of the human mind. (AN 11:10) Also, I like the moniker 'the very-hard-to-see' for the unclouded vision of nibanna. Maybe that's what we should call it if we insist on its reference. (SN 42:1-44)
There's doubtless much more to detail on the subtle stages of unbinding from the four modes of clinging that 'feed the fire' as well as the final chapter on the ‘how’ of it (unsurprisingly, that is the eightfold path), but I'll end this review here.