OCCASION OF REVELATION
The commentators have mentioned two occasions of revelation for this verse and the next seven verses.
First: once Ali (AS) and a number of believers passed by a group of Meccan unbelievers. They laughed at Ali (AS) and the believers and scoffed at them. The above verses were revealed and disclosed their fate on the Day of Resurrection.
Second: the verses are revealed for the people like Ammar, Sahib, Khabbab, Balal and other poor believers who were scoffed by Qureysh unbelievers like Aboujahl, Valid Ebne Moghayreh and Ass Ebne Vael.
However, both commentaries seem quite acceptable.

THEY MOCKED AT BELIEVERS THEN, BUT TODAY ...
VERSES NO.29-36
Following the precedent verses concerned with the great rewards and favors for the righteous, reference is made now to a part of the troubles and problems they suffered in this world for their faith and virtue to clarify that the great rewards are for the great sufferings.
The unbelievers mocked at them in their presence and absence, and called them astray, because they had ignored idolatry which was common among them, and returned towards faith in God and pure monotheism!
However, it was none of their business that to which group and class of people do the believers belong and they were not guardians over them!
On the Day of Resurrection, the situation is reversed, because it is a reflection of man's deeds in the world, and divine justice shall be exercised there. Justice necessitates the pure believers to mock at the obstinate unbelievers. This is a painful chastisement for the arrogant!
The unbelievers are also asked (by God, angels and or the believers) if they are rewarded for their vicious deeds?

THE END OF THE FRAUDULENT SUREH