«إن» may also frame an opponent’s position provisionally and then challenge what follows from it. The rhetorical purpose is not the speaker’s uncertainty, but argument, warning, or indirect rebuke.
«وَإِنْ كُنْتُمْ فِي رَيْبٍ مِمَّا نَزَّلْنَا عَلَى عَبْدِنَا»
If you are in doubt about what We have sent down upon Our servant. (Qurʾān 2:23)
The verse proceeds to challenge those in doubt to produce something comparable. The conditional formulation does not imply that the speaker is uncertain about revelation; it considers the addressees’ stance for the purpose of argument.
In other cases the same construction can expose a flawed assumption or place an ignorant addressee’s claim under examination.