After Allah mentioned the proofs of His creating them, and what they can witness in themselves as proof of that, He mentioned another proof that they can witness, that is, the creation of the heavens and earth. Allah said,
﴿هُوَ الَّذِى خَلَقَ لَكُم مَّا فِى الاٌّرْضِ جَمِيعاً ثُمَّ اسْتَوَى إِلَى السَّمَآءِ فَسَوَّاهُنَّ سَبْعَ سَمَـوَاتٍ﴾
(He it is Who created for you all that is on earth. Then He Istawa ila the heaven and made them seven heavens) meaning, He turned towards the heaven,
(And made them) meaning, that He made the heaven, seven heavens. Allah said,
﴿فَسَوَّاهُنَّ سَبْعَ سَمَـوَاتٍ وَهُوَ بِكُلِّ شَىْءٍ عَلِيمٌ﴾
(And made them seven heavens and He is the Knower of everything) meaning, His knowledge encompasses all His creation, just as He said in another Ayah,
﴿أَلاَ يَعْلَمُ مَنْ خَلَقَ﴾
(Should not He Who has created know) (67:14).