﴿ بَلْ عَجِبْتَ وَيَسْخَرُونَ ﴾

“Nay, but whereas thou dost marvel, they [only] scoff;”

Nay but bal is for effecting a transition from one object to another which in this case is to inform of his state and theirs you marvel ‘ajibta addressing the Prophet s that is you marvel that they deny you while they engage in ridicule at your marvelling