The three forms can carry essentially the same message while differing in emphasis according to the hearer's state.
TypeListenerIllustration
IbtidāʾīUninformedأَخُوكَ قَادِمٌ
ṬalabīUncertain, seeking assuranceإِنَّ أَخَاكَ قَادِمٌ
InkārīDenying the reportوَاللَّهِ إِنَّهُ لَقَادِمٌ
Key point: identify the form by considering both the wording and the listener's communicative situation.