This verse presents a stark warning, linking a specific meditative posture with a tangible consequence—the decay of the physical body. The instruction to hold the dhiya (intelligence, or consciousness) at specific geometric forms – trikona (triangle), chatushkona (square), vrtta (round/rotating), or ākāśa (ether)—immediately evokes the practice of āsana, particularly those designed to create defined shapes within the body. The placement of the manas within these forms is not simply an aesthetic exercise; it’s a precise manipulation of prāṇa and nadī energy. Holding the dhiya in ākāśa, the boundless, all-pervading space, is particularly significant, as it represents a transcendence of the limited self. The absolute certainty (nishaityam) with which the body decays – nasyati – underscores the vital importance of maintaining correct posture and mental focus, suggesting that a misdirected or unstable dhiya disrupts the delicate balance of prāṇic flow, ultimately leading to physical deterioration.