The basic rhetorical force of «إن» (in) is that the condition is not simply presented as a settled occurrence. Its fulfillment remains framed as conditional, even where circumstances may independently make its reality known.
«إن صدقت فماذا تفعل؟»
If you are telling the truth, what will you do?
The speaker puts a claim in conditional form and considers what follows from it. This need not imply that the speaker personally lacks knowledge; one may argue on the hearer’s own supposition.
The force of a conditional particle must be distinguished from the speaker’s actual state of certainty. Conditional language can be used deliberately for argument or rebuke.