﴿ هُوَ ٱلَّذِى يُحْىِۦ وَيُمِيتُ ۖ فَإِذَا قَضَىٰٓ أَمْرًۭا فَإِنَّمَا يَقُولُ لَهُۥ كُن فَيَكُونُ ﴾

“It is He who grants life and deals death; and when He wills a thing to be, He but says unto it, “Be” - and it is.”

He it is Who gives life and brings death. So when He decides upon a matter when He wants to bring something into existence He only says to it ‘Be!’ and it is read fa-yakūnu or fa-yakūna in the subjunctive on account of an implied preceding an. In other words it comes into existence after He has willed it that which is signified by the said words.