Translation:

164. When some of them said: "why do ye preach to a people whom Allah will destroy or visit with a terrible punishment?" Said the preachers: "to discharge our duty to your Lord and perchance they may fear him."

Notes (Tafseer)

1138. There are always people who wonder, no doubt sincerely, what good it is to preach to the wicked. The answer is given to them here: (1) every man who sees evil must speak out against it; it is his duty and responsibility to Allah; (2) there is always a chance that the warning may have effect and save a precious soul. This passage has a special meaning for the times when our Holy Prophet was preaching in Makkah, apparently without results. But it applies to all times.