A Verse That Named a Whole Discipline

Ash-Shams's central claim, that success belongs to the one who 'purifies' the soul (91:9), uses the verbal root zakka, which gave later Islamic spiritual writing its standard technical term, tazkiyat al-nafs, purification of the soul, describing a whole discipline of inward self-examination and moral refinement developed at length in later ethical and Sufi literature, built on this and a small number of related verses rather than elaborated within the Quran's own brief statement itself.

Classical commentators distinguish the verse's claim, that the human is capable of purifying or corrupting the soul, from a purely passive account of moral character, reading it as affirming genuine responsibility for one's own inward state, and later writers on tazkiya developed detailed practical stages and stations of purification that extend far beyond what this compact verse specifies, treating Ash-Shams as the scriptural seed of a tradition it does not itself elaborate. The verse's parallel condemnation of the one who corrupts the soul is read as the necessary counterpart establishing that both outcomes, purification and corruption, are treated by the Quran as within human capacity rather than externally predetermined.