Tafsir of Ash-Shams 91:10

(The Exalted’s saying: "And he has failed who has corrupted it.") The repetition of qad (the particle of verification) is for the purpose of highlighting the importance of verifying its content and signaling that the oath is fundamentally linked to it.

Tazkiyah (purification) means growth (tanmiyah), and tadsiyah (corruption/burial) means concealment (ikhfa). The root of dassa is dassa-sa; the third letter of the identical consonants was replaced with a ya, then it was replaced with an alif because it was mobile and preceded by a fatha. Some have spoken generally, saying a vowel letter was substituted for it, just as they say taqada for taqadada. Dassa-sa is an intensive form of dassa, meaning to hide. A poet said: "And I buried (dassastu) ‘Amr in the dust, and his wives became widows, neglected."

In al-Kashshaf, it is stated that tazkiyah is growth and exaltation, and tadsiyah is diminution and concealment. This means: He has attained every goal and escaped every harm who grew his soul and exalted it through piety—in knowledge and action. And he has indeed lost who diminished it and concealed it through wickedness—in ignorance and immorality.

It is permissible to interpret tazkiyah as purification from the filth of primordial matter (hayula), and tadsiyah as concealing oneself within it and becoming polluted by it. Regardless of the interpretation, in the aforementioned promise and threat—coupled with the Almighty’s swearing by what He swore by—there is that which indicates the knowledge of His existence, the necessity of His essence, the perfection of His attributes, and the mention of the greatness of His bounties and the majesty of His favors. It contains a level of kindness toward His servants that is not hidden.