This is an attack to hypocrisy, on those who cover up their evil-doing by
quoting passages from the Bible or Qur’an. The proverb comes from
Shakespeare’s _The Merchant of Venice_ :

> The devil can cite Scripture for his purpose.
> An evil soul, producing holy witness,
> Is like a villain with a smiling cheek,
> A goodly apple, rotten at the heart:
> Oh, what a goodly outside falsehood hath!

The following, from _Richard III_ , also applies:

> But than I sight; and, with a piece of Scripture,
> Tell them that God bids us do good for evil:
> And thus I clothe by naked villainy
> With old odd ends, stolen out of holy writ;
> And seems a saint, when most I play the devil.