إِنَّ رَبَّهُم بِهِمْ يَوْمَئِذٍ لَّخَبِيرٌۢ
Root: خ-ب-ر. This root occurred in the fourth verse of Sūrat al-Zalzala as well (akhbārahā), and what we recorded there finds its function here.
The core beneath the root: to know a thing by trying it, by looking inside it, by testing it. From the same root come اِخْتِبَار (trial, testing) and خِبْرَة (knowledge gained by experience). The Turkish words hibre (expert appraisal) and haberdar (informed) come from here too; English has no borrowing from this root.
For this reason خَبِير and عَلِيم are not the same thing. ʿAlīm is the one who knows; Khabīr is the one who knows the inner side of the matter. This distinction is regularly drawn in the classical sources: the knowledge of the khabīr is knowledge that comes not from the outside of a thing but from within it.
The verse's word is apt for this reason: the name that comes after the breasts have been sifted is the name of inner knowledge. The ninth verse brought out the outside, the tenth verse sifted the inside, the eleventh verse gave the name of the one who already knew that inside.
A note on the language, and a record. In some dictionaries it is recorded that the word الخَبِير, from the same root, is also used in the sense of "the farmer who ploughs the soil". I pass this report on not as a firm ground but as a recorded usage; since I cannot verify its source and how widespread it is, I have given it no weight in my comment on the sūra's weave of farming. The four-word table above does not rest on this record.
The ordinary word order of the sentence would have been inna Rabbahum la-khabīrun bihim yawmaʾidhin. In the verse بِهِمْ has been drawn in front of the predicate — the same fronting as that of li-Rabbihī in the sixth verse.
The same structure, turned around. In the sixth verse the subject is man and the party brought forward is the Lord. In the eleventh verse the subject is the Lord and the party brought forward is people. The judgement of the sūra and its close are each the other's image in a mirror.
This is another form of the "turning around" we recorded in the section on al-Takāthur: there the one who counted turned into the party about whom questions are asked. Here the one who is ungrateful to his Lord turns into the party of whom his Lord is aware.
A small but decisive detail: the verse does not say bi-aʿmālihim (of their deeds), it says بِهِمْ (of them).
The Qurʾān mostly uses the word khabīr together with deeds: the pattern "God is aware of what you do" occurs many times over. Here, however, the object is not the deed but the person himself.
This accords with the preceding verse. After the breasts have been sifted, what stands there is not a file but a person. When the operation of sifting is over, what is left — what is obtained — is the person himself.
In verses 6, 7 and 8 the sūra was speaking in the singular: al-insān, innahū, innahū. In the eleventh verse it goes over to the plural: Rabbahum, bihim.
The reason for this transition is in the ninth verse: "what is in the graves" — there the subject became plural. The singular that began as the name of the species is distributed, in the scene of the reckoning, among individual persons.
The same movement was there in the preceding sūra as well: al-Zalzala said al-insān (singular) in its third verse and al-nās (plural) in its sixth. Both sūras pass from singular to plural at the same place: in the scene of the reckoning.