Tafsir of An-Nahl 16:40

{إِنَّمَا قَوْلُنَا لِشَيْءٍ} "Our word" is the subject (mubtadaʾ), and "if We intend" (in naqūl) is its predicate (khabar).

{كُن فَيَكُونُ} The verb kāna here is "complete" (tāmma), meaning occurrence and existence. That is: If We intend the existence of a thing, it is nothing but that We say to it: "Come into being," and it comes into being immediately thereafter without delay.

This is a parable illustrating that nothing is impossible for His will, and that its existence upon His—the Exalted—willing it is not delayed, just as the existence of that which is commanded occurs upon the command of an obeyed master when it reaches an obedient, compliant subject. There is no actual speech involved.

The meaning is: Bringing every decreed thing into existence is this easy for Allah—so how could the Resurrection, which is one of those decreed things, be impossible for Him?

It has also been recited as fa-yakūna (in the subjunctive mood), as a conjunction to naqūl (We say).

{وَالَّذِينَ هَاجَرُوا فِي اللَّهِ مِن بَعْدِ مَا ظُلِمُوا لَنُبَوِّئَنَّهُمْ فِي الدُّنْيَا حَسَنَةً ۖ وَلَأَجْرُ الْآخِرَةِ أَكْبَرُ ۚ لَوْ كَانُوا يَعْلَمُونَ * الَّذِينَ صَبَرُوا وَعَلَىٰ رَبِّهِمْ يَتَوَكَّلُونَ}