[Behind them is Hell]—meaning: in front of them. This is an Arabic expression; you say to a man: 'Behind you is such-and-such,' regarding a matter that will come upon him.

Muhammad said: 'Wara'a' (behind) can also mean 'after,' and mention of this has already preceded.

[And what they have earned will not avail them anything]—Al-Hasan's interpretation is: [the good deeds] they performed.