ذَٰلِكَ بِأَنَّ ٱللَّهَ يُولِجُ ٱلَّيْلَ فِى ٱلنَّهَارِ وَيُولِجُ ٱلنَّهَارَ فِى ٱلَّيْلِ وَأَنَّ ٱللَّهَ سَمِيعٌۢ بَصِيرٌ

That is because Allah causes the night to enter into the day and causes the day to enter into the night, and because Allah is Hearing, Seeing.