In the Masnavi, within the context of the grape metaphor, Rumi introduces the concept of the unripenable, stony sour grape (ghooreh-ye sang-bast) to represent the 'original infidel' (kafar-e asli). While most raw souls can be matured and sweetened through the warmth of divine grace and spiritual guidance, some exhibit a permanent, stony obstinacy. Rumi explains that such a soul remains hard, isolated, and permanently unable to dissolve into the collective unity of the 'single juice' (shireh-ye vahed), representing eternal spiritual stagnation and exclusion from the spiritual brotherhood.