The gods of the Idolators are not able to help Them
Allah denounces the idolators for taking the idols as gods alongside Allah, hoping that those gods will help them and provide for them and bring them closer to Allah. Allah says:
لاَ يَسْتَطِيعُونَ نَصْرَهُمْ
(They cannot help them,) meaning, those gods cannot help their worshippers; they are too weak, too insignificant and too powerless. Rather they cannot even help themselves or take revenge on those who want to harm them, because they are inanimate and can neither hear nor comprehend. Allah's saying:
وَهُمْ لَهُمْ جُندٌ مٌّحْضَرُونَ
(but they will be brought forward as a troop.) means, at the time of Reckoning according to the view of Mujahid. This means that those idols will be gathered together and will be present when their worshippers are brought to account, as this will add to their grief and will be more effective in establishing proof against them. Qatadah said:
In the last verse cited above (75), it was said: وَهُمْ لَهُمْ جُندٌ مُّحْضَرُونَ (rather they are an army brought forth for them). One sense of this verse is to take the word: جُندٌ (army) in the text to mean an opponent or adversary and take the verse to mean that the things they have made their objects of worship in the mortal world will turn against them on the Day of Judgment and also bear witness against them.
And according to a Tafsir reported from Hasan and Qatadah رحمۃ اللہ علیہما ، it means that these people had taken to idols as gods in the hope that they would help them. But, the reality on the ground proved to be that they were already incapable of helping them. As a result, the very people who used to worship them as their servants and soldiers are now guarding them to the extent that they would take their side and fight against anyone who opposes them (a1-Qurtubi). The translation given in the text (with brackets) is based on this interpretation.
Tazkirul Quran
Maulana Wahiduddin KhanOn ayahs 76–82
Cattle and other domestic animals are living examples which show that this material world has been created by its Creator in such a way that man should be able to harness it according to his needs. On this amenability of the material world stands the entire structure of human civilization. If horses and bulls were to be as wild as bears and wolves, or if iron and petroleum were to be as uncontrollable as volcanic lava, the evolution of human civilization would become impossible. Therefore, man should be extremely grateful to his Gracious Creator. But, he worships beings other than God and when he is advised to desist, he pays no heed. Undoubtedly, this is the worst type of disobedience to the divine rule, the aftermath of which nobody can escape.
Uthmani text of the Madinah mushaf (King Fahd Complex). Translation: Saheeh International. Tafsir via Quran.com.