إِنِّي أُشْهِدُ اللَّهَ وَاشْهَدُوا أَنِّي بَرِيءٌ مِمَّا تُشْرِكُونَ
I call Allah to witness; you too bear witness that I am free of what you associate with Him. (Hud 11:54)
The first verb “أُشْهِدُ” is declarative, while “اشْهَدُوا” is imperative. The switch gives different roles to the divine witness and the human opponents.
The form moves from a firm declaration to a challenge demanding acknowledgement. The rhetorical value lies in the change of function, not merely in stylistic variety.