( وَقَالُوا مَهْمَا تَأْتِنَا بِهِ مِنْ آيَةٍ لِّتَسْحَرَنَا بِهَا) (And they said, “No matter what sign you bring us with which to bewitch us): They accused Prophet Moses (PBUH) of performing magic whenever he brought them any sign or miracle. In fact, they had already made up their minds not to believe.

( فَمَا نَحْنُ لَكَ بِمُؤْمِنِينَ ) (we will not be believers in you): They refused to believe in him (PBUH), as if they were asked to believe in Prophet Moses (PBUH) himself. True belief is in The Lord of the Prophet Moses (PBUH). Even their way of thinking is wrong, misguided, and misleading.