وَبِالْحَقِّ أَنْزَلْنَاهُ وَبِالْحَقِّ نَزَلَ
We sent it down in truth, and in truth it descended.
The overt phrase «بالحق» is repeated rather than replaced with a pronoun. This keeps the quality of truth prominent in both the act of sending down and the descent itself.
The effect depends on the whole arrangement, including the fronted prepositional phrase and the change in verb. Repetition alone is not a sufficient explanation; what matters is the relationship of the repeated wording to the two stages of the proposition.