M4:107 — چون صفا بیند بلا شیرین شود / خوش شود دارو چو صحت‌بین شود

This beyt comes in a section where Rumi is discussing why prophets and the righteous endure immense suffering. He compares the human soul to raw hide that needs to be 'tanned' through various processes to become soft, beautiful leather. Just as hide must be subjected to bitter and sharp substances and much rubbing to be cleansed and made useful, so too must the human soul undergo afflictions. These 'pains' are not arbitrary but serve a divine purpose: purification (tathīr).

The couplet argues that the perception of this purifying effect or the eventual 'health' makes the suffering sweet. If one understands that the 'affliction' (balā) is leading to spiritual 'purity' (ṣafā), then the pain itself transforms. Similarly, a bitter 'medicine' (dārū) is not only tolerated but 'becomes pleasant' (khush shavad) when the patient 'foresees health' (ṣeḥḥat-bīn shavad). The key is the vision, the inner knowing, that the hardship is a means to a greater, beneficial end. It's a call to accept divine decree and trust in the wisdom behind apparent suffering.