Translation:

18. Of no effect is the repentance of those who continue to do evil until death faces one of them and he says "Now have I repented indeed"; nor of those who die rejecting faith: for them have We prepared a punishment most grievous.

Notes (Tafseer)

526. Note the fine touch. A sin may be fashionable, and people may sin together without compunction. When one of them is faced with Death, he repents, but that sort of repentance is no good.