This book mainly treats the inconceivability of the power of the Dharma by revealing some experience of the author in this field. At the same time, in order to "contrast" the inconceivable, the author also explicated in length the most conceivable worldly Dharmas: that is, the Eight Afflictions, the Eight Winds, and the Four Boundless States of Mind, together with the ways to make contemplations on these.
The reason to treat the inconceivable after going through all kinds of Contemplations in the former two books is this: all Contemplations of any kind are based on language or Concepts represented by Words as the Contemplated; whereas the Mind acts as the Contemplator. Yet be as what it may, these are all within the domain of "the Conceivable." However the Buddha-Dharma, and indeed, even all Dharmas, either worldly or ultra-worldly, in the final analysis, are all inconceivable in their predominant quintessence. In other words, they are, in actuality, beyond the reach of words and thinking, for, as the Sutras usually say, "Such is the real state of the Dharma." Therefore, in the quest of the Supreme Bodhi, one should try all the possible ways conceivable to him to learn and to conquer all the visible hindrances within and without. But in the end, when all the conceivable ways are exhausted, there will still remain huge problems involving SOMETHING inconceivable to the worldly mind, unspeakable to the human tongue, unreachable by the corporeal hand, and intangible to the earthly body. And all these submerged final qualities of all Dharmas can only be comprehended in the light of Wisdom of Buddha Bodhi; otherwise, all things and phenomena will still remain an unsolvable enigma, a pitch-dark cave of ignorance, where all Multibeings plunging into and could never fumble a way out by themselves, save by the guidance of the inconceivable power of Wisdom of the Buddhas and Buddha Dharma.
In fine, what the author means to point out here is that to be a good Buddhist practitioner who aims at the highest Enlightenment, one should not only rely on the tangible experience derived from the Six Senses--the eye, the ear, the nose, the tongue, the body, and the Deliberative Mind--for in the Ten Dharmic Spheres there are far more Dharmas and Phenomena that go way beyond the capacity of terrestrial sensitivity--much more than the naked eye can see, or the ear can hear, or the body can touch. This is especially true of a practitioner (presumably a Bodhisattva) when he has attained to the higher level of practice, and is about to gain access to the Dharmic Sphere (i.e., to become one with the pure original essence of the Dharmic Sphere). Thereupon, all the experience will be beyond the worldly conceivable sensations and perceptions. Therefore, one must practice and build up this higher transcendent capability--viz., the capability to "leave out" or "detach from" the conceivable and the tangible. And one would do this as soon as possible, so as to get ready for the Higher Practice of the Entrance of the Inconceivable Dharmic Sphere, which all great Bodhisattvas (Pusas) should go through prior to their attainment of the Ultimate Supreme Bodhi.