What do the Idolators believe about Their Gods
Allah reproaches the idolators that worshipped others beside Allah, thinking that those gods would intercede for them before Allah. Allah states that these gods do not harm or benefit. They don't have any authority over anything, nor do they own anything. These gods can never do what the idolators had claimed about them. That is why Allah said:
قُلْ أَتُنَبِّئُونَ اللَّهَ بِمَا لاَ يَعْلَمُ فِى السَّمَـوَتِ وَلاَ فِى الاٌّرْضِ
(Say: `Do you inform Allah of that which He knows not in the heavens and on the earth') Ibn Jarir said: "This means, `Are you telling Allah about what may not happen in the heavens and earth' Allah then announced that His Glorious Self is far above their Shirk and Kufr by saying:
سُبْحَانَهُ وَتَعَالَى عَمَّا يُشْرِكُونَ
(Glorified and Exalted is He above all that which they associate as partners (with Him)!)
Shirk is New
Allah then tells us that Shirk was new among mankind. It was not in existence in the beginning. He tells us that people were believers in one religion and that religion was Islam. Ibn `Abbas said: "There were ten centuries between Adam and Nuh. They were all on Islam. Then differences among people took place. They worshipped idols and rivals. So Allah sent extensive evidence and irrefutable proof with His Messengers."
لِّيَهْلِكَ مَنْ هَلَكَ عَن بَيِّنَةٍ وَيَحْيَى مَنْ حَىَّ عَن بَيِّنَةٍ
(So that those who were to be destroyed (for rejecting the faith) might be destroyed after a clear evidence, and those who were to live might live after a clear evidence.)8:42 Allah's statement:
وَلَوْلاَ كَلِمَةٌ سَبَقَتْ مِن رَّبِّكَ
(And had not it been for a Word that went forth before from your Lord...) means that if Allah had not decreed He would not punish anyone until the evidence is established against them. And also that if He had not given creatures a respite until a defined term had passed, He would have judged among them in what they disputed. Then He would have caused the believers to be happy and delighted and the disbelievers to be miserable and wretched.
Tafsir Ibn Kathir (abridged, English).