إِنَّا زَيَّنَّا ٱلسَّمَآءَ ٱلدُّنۡيَا بِزِينَةٍ ٱلۡكَوَاكِبِ
Indeed, We have adorned the nearest heaven with an adornment of stars.
Here Allah describes with what beauty and adornment (زِينَةٍ) He has decked out the first heaven, the one nearest to us.
The word كَوَاكِبِ here can refer both to the stars and to the planets among those celestial bodies that light up our night sky.
But this beauty serves a purpose beyond merely aesthetic concerns. These celestial bodies are not just ornaments; they are also part of an advanced defense system.
The jinn are confined to this lowest heaven; they cannot rise to the higher realms beyond the first heaven, where the angels dwell and where divine knowledge is found. When the angels descend to earth with commands of revelation or punishment, they must pass through this first heaven, and at that time the jinn try to eavesdrop on their conversations.
The heavens are guarded against the devils’ attempts to secretly learn news of the unseen.