ولقد آتينا موسى الكتاب فاختلف فيه
And indeed We gave Musa the Scripture, but dispute arose therein.
means, they disbelieved in him and did not show him any respect
فاصبر كما صبر أولوا العزم من الرسل
Therefore be patient as did the Messengers of strong will, (46:35)
ولوﻻ كلمة سبقت من ربك
And had it not been for a Word that went forth before from your Lord,
i.e., to delay the Reckoning until the Day of Resurrection,
لقضي بينهم
the matter would have been settled between them.
means, the punishment would have been hastened for them. But they have an appointed time, beyond which they will find no escape.
وإنهم لفي شك منه مريب
But truly, they are in grave doubt thereto.
means, their words of disbelief are not due to any wisdom or insight on their part; rather they spoke without any attempt at examining it thoroughly.
This was also the interpretation of Ibn Jarir, and it is a plausible interpretation. And Allah knows best