The transient nature of the world and human duality
Nahj al-Balāgha|Volume 1|Book 3|Chapter 133
١٣٣. وَقَالَ (عليه السلام): الدُّنْيَا دَارُ مَمَرٍّ لَا دَارُ مَقَرٍّ وَالنَّاسُ فِيهَا رَجُلَانِ رَجُلٌ بَاعَ فِيهَا نَفْسَهُ فَأَوْبَقَهَا وَرَجُلٌ ابْتَاعَ نَفْسَهُ فَأَعْتَقَهَا.
133. Amīr al-mu’minīn, peace be upon him, said: This world is a place for transit, not a place for stay. The people herein are of two categories. One is the man who sold away his self (to his passions) and thus ruined it, and the other is the man who purchased his self (by control against his passions) and freed it.