Al-Waqiʿa 56:79: لَا يَمَسُّهُ إِلَّا الْمُطَهَّرُونَ
None but the purified touch it.
Just as God, the Pure and Holy, permits none but those in a state of purity to touch His pure Word, so too He permits none but pure souls to attain the inner truths, mysteries and essence of the Qur’an.
Just as the Qur’an’s words cannot be touched by impure hands, the impure cannot comprehend its allusions, subtleties, truths, stars and inner depths. Full and complete understanding of the Qur’an is possible only through absolute purity. Only those whom God has affirmed as belonging to the Verse of Purification have access to this distinction; others will draw from the vast ocean of the Qur’an according to their degree of purity.
... Umar ibn al-Khattab sent me during his caliphate to ʿAli ibn Abi Talib, peace be upon him, saying, “I wish to compile the Qur’an in a codex, so send us what you have written of the Qur’an.” He replied, “By God, you will strike off my head before you get it.” I asked, “Why?” He said, “Because God says, لَا يَمَسُّهُ إِلَّا الْمُطَهَّرُونَ—meaning, none but the purified can attain it in its entirety. By ‘the purified,’ He means us: we are those from whom God has removed all defilement and whom He has purified completely. And He says, ‘Then We gave the Book in inheritance to those of Our servants whom We chose.’ We are those whom God chose from among His servants. We are God’s elect; the parables were set forth for our sake, and the revelation descended upon us.”
Kitāb Sulaym ibn Qays al-Hilālī, vol. 2, p. 847