تَبَارَكَ ٱلَّذِى جَعَلَ فِى ٱلسَّمَآءِ بُرُوجًا وَجَعَلَ فِيهَا سِرَٰجًا وَقَمَرًا مُّنِيرًا · وَهُوَ ٱلَّذِى جَعَلَ ٱلَّيْلَ وَٱلنَّهَارَ خِلْفَةً لِّمَنْ أَرَادَ أَن يَذَّكَّرَ أَوْ أَرَادَ شُكُورًا
"Blessed is He who set constellations in the sky and placed in it a lamp and an illuminating moon! And it is He who made the night and the day follow one after the other: for whoever wishes to take heed or wishes to give thanks."
بُرُوج — treated in al-Burūj on the occasion of the sūra's name (the root's sense of "a visible, high structure"). I do not repeat it here.
خِلْفَة — root خ-ل-ف: to come one after another, the one taking the other's place. The root was treated at Fāṭir 35/39 (khalāʾif).
I record this as my own reading, and its ground is the repetition of the verb: arāda (he willed) occurs twice — once for remembering, once for thanks. That is, the alternation of night and day is offered as an opportunity: an order in which one who has missed it can make it up. And both verbs state will: the order works the same for everyone, and the benefit from it is tied to wanting it.