"Or have We sent down to them an authority," meaning: a proof, "that speaks," meaning: that authority speaks, "of that which they were associating [with Him]," meaning: no proof has been sent down to them regarding that, commanding them to associate partners [with God].
﴿أم أنزلنَا عَلَيْهِم سُلْطَانا﴾ أَي: حجَّة ﴿فَهُوَ يتَكَلَّم﴾ أَيْ: فَذَلِكَ السُّلْطَانُ يَتَكَلَّمُ ﴿بِمَا كَانُوا بِهِ يشركُونَ﴾ أَيْ: لَمْ تَنْزِلْ عَلَيْهِمْ حُجَّةٌ بذلك تَأْمُرهُمْ أَن يشركوا
