Surah An Nur Tafseer

يُقَلِّبُ اللَّهُ اللَّيْلَ وَالنَّهَارَ

Allah causes the night and the day to succeed each other.

He is controlling them, so that He takes something from the length of one and adds it to the other, which is short, until they become equal, then He does the opposite so that the one which was short becomes long and vice versa. Allah is the One Who is controlling that by His command, power, might and knowledge.

إِنَّ فِي ذَلِكَ لَعِبْرَةً لاُِّوْلِي الاَْبْصَارِ

Truly, in this is indeed a lesson for those who have insight.

means, this is an indication of His greatness, may He be exalted.

This is like the Ayah:

إِنَّ فِى خَلْقِ السَّمَـوَتِ وَالاٌّرْضِ وَاخْتِلَـفِ الَّيْلِ وَالنَّهَارِ لاّيَـتٍ لاٌّوْلِى الاٌّلْبَـبِ

Verily, in the creation of the heavens and the earth, and in the alternation of night and day, there are indeed signs for men of understanding. (3:190)