Rasul Allah (sal Allahu alaihi wa sallam) said: “If you knew what I know you would laugh a little and cry a lot!”
Once Hasan al-Basri passed by a man who was laughing and asked him: “Oh my nephew! Have you safely passed over the Sirat (bridge over Hell)?” He replied, “No.” Hasan al-Basri asked: “Have you received news whether you will end up in Paradise or Hell?” The man replied that he hadn’t. So Hasan al-Basri asked, “Why do you laugh then, may Allah save you, while the matter ahead is horrifying?” That man was never seen laughing until he died. (But he smiled as this is a part of the Sunnah of the Prophet.) [Al-Hasan Al-Basri p.89, quoted in Silent Moments by Abdul-Malik Al-Qasim]
The horror of Jahannum is such that one look at it will have a man willing even to throw his children, his wife, his brother, his parents, and his entire clan into it if by doing so he can escape himself. We cannot imagine throwing our children into any fire on earth to escape it ourselves, yet this is what people will be doing as a result of just a glance at Jahannum. Fear will make us mindless!
On the Day of Judgment Allah (subhana wa ta’ala) will ask a sinner whether he would like to ransom himself from the Fire by giving equivalent to the weight of the world in gold. The sinner will readily agree to give twice as much. Then Allah (subhana wa ta’ala) will say: Did I not ask you for something much less than this in the world? Only a few sujood, only to make your guest feel welcome, only to say ‘La ilaha ilAllah’? Unfortunately, the most ordinary and easy task seems difficult to us because we don’t see Jahannum before our eyes. But when we do see it with our eyes it will be too late to do anything