إِنَّ رَبَّهُمْ بِهِمْ يَوْمَئِذٍ لَخَبِيرٌ
Indeed their Lord will be fully aware of them on that Day. (100:11)
Inna, the lām of la-khabīr, and the fronting of bihim reinforce divine awareness and its object. Yawmāʾidhin singles out the day when the consequences of deeds are manifested. It does not mean that God first acquires knowledge on that day; divine knowledge is not limited to the Day of Judgment.
The surah has moved from rapid external motion to the hidden moral state of human beings and finally to resurrection. The emphatic closing assertion gathers those themes under divine knowledge and brings the passage to a forceful conclusion.