ما المقسم عليه في سورة الشمس؟

The subject of the oath in Surat Ash-Shams is the success of those who purify and cleanse their souls, and the loss of those who corrupt and debase them with sins. Allah swore seven times by cosmic signs (the sun, the moon, the night, the day, the sky, the earth, and the human soul) upon the success of those who purify themselves and the failure of those who corrupt it. The answer to the oath is in His saying, ﴿قَدْ أَفْلَحَ مَنْ زَكَّاهَا﴾ (He has succeeded who purifies it), and its تقدير (implied meaning) is: Indeed, he has succeeded. "زكاها" (purifies it) means cleanses it and develops it with good deeds, and "دسّاها" (corrupts it) means hides it and debases it with sins.