"Indeed, they will not avail you at all against Allah," meaning: if you were to follow their whims, He would punish you, and they would not avail you at all. Allah, however, has [protected] him from that, and decreed that he remain upon what he is on. "And indeed, the wrongdoers"—the polytheists—"are allies of one another" in the worldly life, while they are enemies in the Hereafter; they will disown one another.
﴿إِنَّهُمْ لَنْ يُغْنُوا عَنْكَ مِنَ الله شَيْئا﴾ أَي: إِن اتبعت أهواءهم عذَّبتك وَلم يغنوا عَنْك شَيْئا، وَقد [عصمه] الله من ذَلِك، وَقضى أَن يثبت على مَا هُوَ عَلَيْهِ ﴿وَإِن الظَّالِمين﴾ الْمُشْركين ﴿بَعضهم أَوْلِيَاء بعض﴾ فِي الدُّنْيَا، وهم أعداءٌ فِي الْآخِرَة؛ يتبرَّأُ بعضُهم من بعض.