A second answer: The Qur'an's aim is not to teach the history of creation; it was revealed to teach knowledge of the Maker, and so contains different levels (maqâmat). When describing the [divine] bounties, favours, and mercy and the clarity of the evidences, the earth comes first. But on the level of the proofs of [divine] grandeur, sublimity, and power, the heavens precede.
"Then (thumma):" this may refer to 'a being protracted' or procrastination (tarâkhi). This may be essential (dhâti), and may also pertain to degree (rutbî) [or to reflection (tafakkurî)]. Thus "and (lit. then) has applied His design (thumma astawâ)" implies the unstated words "Then know and reflect on [how] He applied His design to the heavens ..." [That is, the creation of the heavens was first in time but in respect of reflection and thought it is in second place; and the creation of the earth was after that of the heavens but in regard to reflective thought it comes first.]1
The Third Matter, regarding "seven (sab'a)."
Consider this: ancient philosophy asserted that the heavens were ninefold, and its proponents conceived of it in an extraordinary form. Their ideas dominated mankind for centuries. In fact, very many Qur'anic commentators were forced to bend the literal meanings of verses to [conform with] with their school. Modern science, however, asserts that the stars are suspended in space or in the void, as though it denies the existence of the heavens. That is to say, one went to one extreme and the other went to the other. As for the Shari'a, it states that the Maker (May His glory be exalted) created seven heavens and placed the stars in them like fish swimming [in the sea]. The Hadith "The heavens are a wave held back"2 alludes to this. This school [of thought] may be verified on six levels:
The First: It has been established by science and philosophy that endless space is filled with ether.
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1.See, İsârâtu'l-İ'caz [Abdûlmecid], 265.
2.Musnad, ii, 370; al-Tirmidhi, Sura al-Hadid, 1 (no: 3298). For further details see, Ishârât al-l'jâz [Ihsân Qasim], 226.