وَيَوْمَ نَحْشُرُهُمْ جَمِيعًا ثُمَّ نَقُولُ لِلَّذِينَ أَشْرَكُوا۟ مَكَانَكُمْ أَنتُمْ وَشُرَكَآؤُكُمْ فَزَيَّلْنَا بَيْنَهُمْ · هُنَالِكَ تَبْلُوا۟ كُلُّ نَفْسٍ مَّآ أَسْلَفَتْ
"On the day We gather them all together, then say to those who associated others with God: 'Stay where you are, you and your partners' — We part them from one another. Their partners say: 'It was not us you were serving. God suffices as a witness between us and you; we were indeed unaware of your serving us.' · There every soul will test out what it sent on ahead. They are brought back to God, their true Master, and what they invented is lost to them."
مَكَانَكُمْ — a noun functioning as a verb (ism fiʿl) in the imperative: "stay where you are, stand still." I record this as an observation about the word order: the scene is set up like a courtroom, and the first command is to halt.
فَزَيَّلْنَا بَيْنَهُمْ — root ز-ي-ل: to separate, to open a space between. The verb is in Form II and states repetition or intensity: We parted them thoroughly.
And this parting will come back once more in the sūra, with another word: in the twenty-eighth verse the partners speak, and in the thirtieth wa ḍalla ʿanhum mā kānū yaftarūn — "what they invented was lost to them".
In Arabic the fronting of the object states specification. The sentence, that is, is not "you were not serving us" but, more exactly: "it was not us you were serving" — you were serving someone else.
I record this as my own reading, and its ground is this fronting: the partners' defence is not that there was no serving but that it was not directed to them. And the same scene was treated in Sabaʾ and at Maryam 19/81-82: the side supposed to have been turned to does not acknowledge the turning.
تَبْلُوا۟ كُلُّ نَفْسٍ مَّآ أَسْلَفَتْ — the root ب-ل-و: to try, to wear out by testing. The root was analysed at al-Baqara 2/49 (balāʾun min rabbikum ʿaẓīm) and it was recorded there: the word covers testing by good as well. I rely on that treatment.
And the subject of the verb must be recorded: tablū kullu nafsin — the one who tests is the soul itself. And what is tested is what it itself sent on ahead.
I record this as my own reading, and its ground is the subject of the verb: in this scene no one tests anyone else — each searches through his own past. And this completes the parting in the preceding sentence: once the partners are gone, nothing remains but one's own deed.
أَسْلَفَت — root س-ل-ف: to go before, to send on ahead. Salaf — those who went before. In commercial usage the word also carries the sense of "paid in advance": the salam contract. And this picture fits the verse: what was sent on beforehand and whose return will be taken later.
مَوْلَىٰهُمُ ٱلْحَقِّ — and the backbone word of the sūra occurs here as a qualifier: "their true Master". What stands opposite it is said at once: wa ḍalla ʿanhum mā kānū yaftarūn — what they invented. That is, ḥaqq and iftirāʾ stand face to face in the same sentence.