«كَلَّا سَوْفَ تَعْلَمُونَ ثُمَّ كَلَّا سَوْفَ تَعْلَمُونَ»
No indeed—you will come to know; again, no indeed—you will come to know.
Sawfa points to the future, while kallā conveys rebuke or deterrence. Repeating the construction strengthens the sense of warning and certainty.
The recurrence is not dispensable filler: repetition itself contributes to rhetorical force. The wording, however, does not license inventing additional historical details.