After that it was said: فَلْيَضْحَكُوا قَلِيلًا (So, let them laugh a little, and weep a lot, being a reward of what they used to earn — At-Tawbah 9:82 ⧉). Though, the word ` falya dhak u' (So, laugh) has been used in the imperative form, but commentators interpret it in the sense of the predicate of a nominal clause. The wisdom behind the use of the imperative form given by them is that this is categorical and certain. In other words, this is going to happen as a matter of certainty. Such people could laugh for the days they have in the mortal world - but, in 'Akhirah, they must weep and weep forever.
Commentator Ibn Abi Hatim reports the explanation of this verse At-Tawbah 9:82 ⧉ from Sayyidna ` Abdullah ibn ` Abbas ؓ as follows:
اَلدُنیِا قلیلُ فَلیَضحکُوا فِیھَا مَاشَآُء وافاِذَا انقَطعتِ الدُّنیَا و صَارُوآ اِلٰی اللہِ فَلیَستَانِفُوافلیستانِفُوا البُکَاءَ بُکَاًء لَا یَنقَطِع اَبَداً
The dunya (present world) is short-lived. So, let them laugh therein as they wish but when ` dunya will come to an end and they will start coming to Allah, then, they will start weeping, a weeping which will never come to an end. (Mazhari)