"Whoever does righteousness, it is for his own soul," meaning: he will find it with Allah. "And whoever does evil, it is against it," meaning: it is against his own soul.
Interpretation of Surah al-Jathiyah from verse 16 to verse 17.
﴿من عمل صَالحا فلنفسه﴾ أَي: يجده عِنْد الله ﴿وَمَنْ أَسَاءَ فعلَيْهَا﴾ أَي: فعلى نَفسه.
تَفْسِير سُورَة الجاثية من الْآيَة ١٦ إِلَى آيَة ١٧.