﴿ فَلْيَضْحَكُوا۟ قَلِيلًۭا وَلْيَبْكُوا۟ كَثِيرًۭا جَزَآءًۢ بِمَا كَانُوا۟ يَكْسِبُونَ ﴾

“Let them, then, laugh a little - for they will weep a lot in return for what they have earned.”

But let them laugh a little in this world and weep much in the Hereafter as a requital for what they used to earn the sentence is predicative of their state expressed in the form of an imperative.