وَكَذَٰلِكَ فَتَنَّا بَعْضَهُم بِبَعْضٍ لِّيَقُولُوٓا۟ أَهَٰٓؤُلَآءِ مَنَّ ٱللَّهُ عَلَيْهِم مِّنۢ بَيْنِنَآ · وَإِذَا جَآءَكَ ٱلَّذِينَ يُؤْمِنُونَ بِـَٔايَٰتِنَا فَقُلْ سَلَٰمٌ عَلَيْكُمْ كَتَبَ رَبُّكُمْ عَلَىٰ نَفْسِهِ ٱلرَّحْمَةَ
"Thus We tried some of them by means of others, so that they would say: 'Is it these whom God has favoured from among us?'… And when those who believe in Our signs come to you, say: 'Peace be upon you! Your Lord has written mercy upon Himself.'"
The ground of the command in the fifty-second verse (not to drive away) is given here: fatannā baʿḍahum bi-baʿḍ — a trying of them by one another.
And the concept of fitna was treated at al-Anfāl 8/25 and al-Kahf 18/7. The difference here must be recorded: the instrument of trial is neither property nor an event — it is people.
I record this as my own reading, and its ground is the sentence transmitted: a-hāʾulāʾi manna'llāhu ʿalayhim min bayninā — "is it these, from among us?" The objection is about to whom what was given was given. And the same logic was treated at al-Aḥqāf 46/11 (law kāna khayran mā sabaqūnā ilayh) and at al-Zukhruf 43/31.
The expression kataba ʿalā nafsihi'r-raḥma had occurred in the 12th verse of this sūra. The two occurrences are a repetition that can be verified within the sūra — and both come in a context of inclusiveness.
قُلْ إِنِّى نُهِيتُ أَنْ أَعْبُدَ ٱلَّذِينَ تَدْعُونَ مِن دُونِ ٱللَّهِ (56) — the same sentence was treated at Ghāfir (al-Muʾmin) 40/66; I rely on that treatment.