Translation:

17. Say: "Who is it that can screen you from Allah if it be His wish to give you Punishment or to give you Mercy?" Nor will they find for themselves besides Allah any protector or helper.

Notes (Tafseer)

3688. It is still worse if the cowardice or desertion is shown in a Cause, which, because of the high issues of truth and justice, may be called the Cause of Allah. How can any one escape Allah's Punishment? And in the same way, how can any one prevent another from obtaining Allah's Mercy by repentance and amendment? The better path, therefore, is to stand firm in Allah's Way, and if you fail through human weakness, to repent and seek Allah's Mercy. Cf. xxxiii. 24, and n. 3698 below.