Commentary
Sayyidna ` Abdullah ibn ` Abbas ؓ has said that one of the distinctions of Surah Al-An'am is that the whole of it, except some 'Ayat, was revealed at one time in Makkah with the complement of seventy thousand angels following it with recitation of the name of Allah. Early Tafsir authorities Mujahid, al-Kalbi, Qatadah and others have said more or less the same thing.
Abu Ishaq Al-Asfra'ini has said that this Surah consists of all principles and subsidiaries of Tauhid (Oneness of Allah). This Surah has been prefaced with الْحَمْدُ لِلَّـهِ (Al-Hamdulillah) whereby people have been told that all praises belong to Allah. The purpose is to educate and help people get the right perspective - that Allah needs no praise from anyone, whether or not anyone praises Him, He is, in terms of His own intrinsic perfection, by Himself, the Praised One. By bringing in the sentence which follows immediately, which mentions the creation of the heavens and the earth and the darkness and the light, given there is the very proof of His being the Praised One. Isn't it that the Being which holds such Power and Wisdom would have to be the One deserving of all praise?
In this verse, ` samawat' (heavens) has been mentioned in the plural while 'ard (earth), in the singular - though, in another verse (65:12), earth has been identified as being seven like the heavens. Perhaps, it is indicative of the mutual distinction the seven heavens have in terms of their form and attributes while the seven earths are like each other, therefore, they were taken as one in number. (Mazhari)
Similarly, by mentioning ` zulumat' (darkness, or layers of darkness) in the plural, and 'nur' (light) in the singular, the indication given may be that nur or light signifies the correct way and the straight path - and that is just one, while zulumat, or many layers of darkness, signifies the path of error - and their number runs in thousands. (Mazharl al-Bahr al-Muhit)
Also noticeable here is that the origination of the heavens and the earth has been expressed through the word, 'khalaqa' (created) while that of darkness and light with the word, ja‘ala' (made). The hint implied is that darkness and light are not independent and self-existent like the heavens and the earth, instead, they are contingents and attributes. And zulumat (darkness) has been given precedence over nur (light) perhaps because zulumat is basic to this world while nur is associated with particulars - when they are there, there is light; and when they are not there, there is darkness.
By pointing out to the reality of Tauhid (Oneness of Allah) and its open proof in this verse the purpose is to warn all those peoples who do not simply believe in Tauhid, or have forsaken the reality of Tauhid despite professing it.
The Magians (Majus) believe in two creators, Yazdan and Ahriman (or Ahraman). Yazdan, according to them, is the creator of good and Ahriman, the creator of evil. They also identify these as (the principles of) light and darkness.
The polytheists in India take an incredibly high number of gods as partners in the divinity of God. The Arya Samajists, despite acknowledging Tauhid, take spirit and matter to be infinitely pre-existent, and independent of the power and creation of God, whereby they have moved way away from the reality of Tauhid. Similarly, the Christians who, despite professing the creed of Tauhid, started taking Sayyidna ` Isa (علیہ السلام) and his blessed mother as partners in the divinity of God - and then, in order to prop their belief in one God, they to rely on the irrational theory of Unity in Trinity. As for the disbelievers and polytheists of Arabia, they demonstrated such philanthropy in dishing out Godhood that, according to them, every piece of rock on a hill could be good enough to become an object of worship for the whole human-kind! Thus, the wonderful human being whom Allah had made to be the noblest of His creation, someone whom the whole universe was to serve, went so astray from the right path that he took - not just the moon, the sun, the stars, but the fire, water, trees and rocks too - even crawling insects as objects of prostration and worship, providers of needs and resolvers of problems.
By saying in this verse of the Holy Qur'an that Allah Ta` ala is the Creator of the heavens and the earth and He is the Maker of darkness and light, all such false notions have been refuted - when He is the sole Creator and Maker of everything, ascribing partners to His Divinity makes no sense.