أَلَيْسَ ٱللَّهُ بِكَافٍ عَبْدَهُ ۖ وَيُخَوِّفُونَكَ بِٱلَّذِينَ مِن دُونِهِ ۚ وَمَن يُضْلِلِ ٱللَّهُ فَمَا لَهُ مِنْ هَادٍ

The Prophet Muhammad preached the Unity of God. But he did not stop at only the positive declaration of ‘God is one’. At the same time he used to negate those non-godly beings whom the people themselves had given the status of deities. This second part of his mission had become unbearable to the people. Those non-godly beings were, in fact, their national heroes. For centuries exaggerated tales of their miraculous deeds had held the people in thrall. The greatness of these beings had captured people’s minds to such an extent that when the Prophet Muhammad contradicted the idea of their holiness, they could not understand how they could be other than holy. They asked the Prophet Muhammad to desist from speaking against their gods, otherwise they warned that he would be destroyed. The preacher of Truth was ordered not to pay heed to remarks of this kind, and to continue to perform the dual task of advocating the Unity of God and rejection of polytheism—all this while relying up on God and praying for the Truth to become clear and manifest.

— Source: Tazkirul Quran (Maulana Wahiduddin Khan) via Quran.com (39:36)