In Book Four, Section 93 of the Masnavi, Jalal al-Din al-Rumi employs the metaphor of polishing iron to describe spiritual purification. He compares the physical, earthly body (تن خاکی) to a piece of dark, unpolished iron. Through spiritual discipline—specifically, curbing sensual desires (هوا) and employing God-given intellect (عقل) as a polisher—this dark iron can be transformed into a bright mirror. Once polished, the heart and body lose their physical density and become capable of reflecting the unseen spiritual realm (اشکال غیبی), allowing the seeker to directly witness angels, paradise, hell, and the resurrection in this world rather than merely imagining them.