Doubt and spiritual heedlessness

وَلَقَدْ ءَاتَيْنَا مُوسَى ٱلْكِتَـٰبَ فَٱخْتُلِفَ فِيهِ ۗ وَلَوْلَا كَلِمَةٌ سَبَقَتْ مِن رَّبِّكَ لَقُضِىَ بَيْنَهُمْ ۚ وَإِنَّهُمْ لَفِى شَكٍّ مِّنْهُ مُرِيبٍ

And We had already given Moses the Scripture, but it came under disagreement. And if not for a word [i.e., decree] that preceded from your Lord, it would have been concluded between them. And indeed they are, concerning it [i.e., the Qur’ān], in disquieting doubt.