لَّكِنِ اللَّهُ يَشْهَدُ بِمَا أَنزَلَ إِلَيْكَ أَنزَلَهُ بِعِلْمِهِ وَالْمَلَائِكَةُ يَشْهَدُونَ وَكَفَى بِاللَّهِ شَهِيدًا
But Allah bears witness to what He has sent down to you—He sent it down with His knowledge—and the angels bear witness [too], and Allah quite suffices as witness.
Agha Ali Puya Commentary
Commentary on Quran 4:166
[Pooya/Ali Commentary 4:166] Allah's testimony is the convincing force of the Quran, which represents His knowledge.