(… ثُمَّ ارْجِعِ الْبَصَرَ كَرَّتَيْنِ) (Then return [your] vision twice again. …): Meaning, even if you have looked many times, you will not find any defect or crack. If you are not certain from the first look, you can look once again carefully and repeatedly, the result is that your sight will return to you humbled and weak, cannot bear the strong light, same as when you try to look at the sun so that its light will prevent you from seeing, because light is intended to enable us to see which cannot be seen.

(  يَنقَلِبْ إِلَيْكَ الْبَصَرُ خَاسِئًا وَهُوَ حَسِيرٌ… ) (…vision will return to you humbled while it is fatigued): The vision will return to you humbled, and humiliated because you did not see what he wants from the cracks and defect. Not only that but with fatigue and regret for losing what you want.