وَلَا تَسُبُّوا۟ ٱلَّذِينَ يَدْعُونَ مِن دُونِ ٱللَّهِ فَيَسُبُّوا۟ ٱللَّهَ عَدْوًۢا بِغَيْرِ عِلْمٍ
"Do not revile those they call upon besides God, lest they revile God in enmity, without knowledge."
The verse lays down a prohibition and gives its ground by way of its consequence: fa-yasubbu'llāha ʿadwan bi-ghayri ʿilm.
I record this as my own reading, and its ground is the letter fāʾ: the prohibition is tied, before the wrongness of the reviling itself, to the response it will produce. That is, the measure is laid down with the other side's reaction taken into account.
And the same field was treated at al-ʿAnkabūt 29/46 (bi'llatī hiya aḥsan), at Fuṣṣilat 41/34 (idfaʿ bi'llatī hiya aḥsan) and at al-Anʿām 6/68 (fa-aʿriḍ ʿanhum). The four verses together set up a method: the form of dispute, the form of response, the limit of keeping away, and the limit of speech.
كَذَٰلِكَ زَيَّنَّا لِكُلِّ أُمَّةٍ عَمَلَهُمْ — and what follows states that everyone sees his own doing as fine. The verb tazyīn was treated at Fāṭir 35/8, Ghāfir (al-Muʾmin) 40/37 and al-Anfāl 8/48; here the agent is named openly and the scope is given as "every community".