فَلْيَضْحَكُواْ قَلِيلً

So let them laugh a little...

Ibn Abi Talhah reported that Ibn Abbas commented,

"Life is short, so let them laugh as much as they like in it. But when life ends and they are returned to Allah, the Exalted and Most Honored, they will start crying forever without end."
 
وَلْيَبْكُواْ كَثِيرًا جَزَاء بِمَا كَانُواْ يَكْسِبُونَ
 
 

and (they will) cry much as a recompense of what they used to earn (by committing sins).