Overall meaning : Say, Muhammad, to the idolaters, ‘How can you disbelieve in Allah, who created the earth in two days?! How can you set up equals and rivals that you worship besides Him?! He is the Lord of all the worlds!’
He placed on the earth firmly-rooted mountains rising above its surface, bestowed His blessings on it, and ordained all its means sustenance in another two days—totalling four days exactly, neither less nor more (That is, including the former two days in which He created the earth). We have clarified this for those who ask about how long it took to create the earth and all that is in it.
Then, turning to the heaven, which was then just smoke, He said to it and to the earth after He had created them, ‘Submit to Me, willingly or unwillingly.’ They said, ‘We submit willingly.’ He formed the heaven into seven heavens in two days, and to each heaven He assigned its task and whatever creation and management He willed. He adorned the lowest heaven with shining stars and with them He has guarded it against the devils that attempt to eavesdrop on the highest assembly of the angels. Such is the design of the All-Mighty, the All-knowing.