تَنزِيلًا مِّمَّنْ خَلَقَ ٱلْأَرْضَ وَٱلسَّمَٰوَٰتِ ٱلْعُلَى · ٱلرَّحْمَٰنُ عَلَى ٱلْعَرْشِ ٱسْتَوَىٰ · لَهُۥ مَا فِى ٱلسَّمَٰوَٰتِ وَمَا فِى ٱلْأَرْضِ وَمَا بَيْنَهُمَا وَمَا تَحْتَ ٱلثَّرَىٰ
Tanzīlan mimman khalaqa'l-arḍa wa's-samāwāti'l-ʿulā · Ar-Raḥmānu ʿala'l-ʿarshi'stawā · Lahu mā fi's-samāwāti wa mā fi'l-arḍi wa mā baynahumā wa mā taḥta'th-tharā
"A sending down from the One who created the earth and the high heavens. · The Merciful has mounted the throne. · To Him belongs whatever is in the heavens, whatever is on the earth, whatever is between the two, and whatever is beneath the soil."
A point of word order is worth recording: the verse names al-arḍ (the earth) before al-samāwāt (the heavens).
The usual order in the Qurʾān generally runs from the heavens down to the earth (khalaqa's-samāwāti wa'l-arḍ). Here it is reversed.
I record this as an observation and make no claim about intent: the sentence begins from the ground under the feet of the one addressed and climbs upward; and in the sixth verse it goes further down still: wa mā taḥta'th-tharā — beneath the soil.
ٱلثَّرَىٰ — root ث-ر-ي: moist earth, damp ground. The lexicographers record that the word is used not of dry earth (turāb) but of earth holding moisture in it. The word occurs only here in the Qurʾān.
And four layers are counted: the heavens, the earth, what is between the two, what is beneath the soil. The same technique of "covering every direction" was treated at al-Qaṣaṣ on 28/1-6 and at Maryam on 19/64; I rely on those treatments. The difference here is that a fourth layer has been added — the scope is widened not only upward but downward as well.
On this expression I enter a note per the method (Method) and do not open the discussion.
The same expression was treated at al-Sajda on 32/4, and two positions were tabulated there — tafwīḍ (the wording is accepted as it stands and its modality is committed to God) and taʾwīl (it is interpreted as the establishing of sovereignty). Both are transmitted; I do not impose a preference. I rely on that treatment and do not repeat it here. The common principle is al-Shūrā 42/11.
The only thing that belongs here is the choice of subject, and this is a datum of the text: the subject of the sentence is al-Raḥmān.
This expression occurs in seven places in the Qurʾān (al-Aʿrāf 7/54, Yūnus 10/3, al-Raʿd 13/2, Ṭāhā 20/5, al-Furqān 25/59, al-Sajda 32/4, al-Ḥadīd 57/4) and in most of them the subject is Allāh or a pronoun. There are two places where it is built with the name al-Raḥmān: here and al-Furqān 25/59. This is a datum that can be counted.
I record this as my own reading, and its ground is the distribution above: the subject of the sentence that declares sovereignty has been made the name that declares mercy. And it was treated at Maryam how this name forms the spine of a sūra; in Ṭāhā the name occurs four times (5, 90, 108, 109) and all four are in a scene of power: the throne, Aaron's reminder before the calf, the day the voices fall silent, the moment intercession is made conditional on permission. This distribution can be verified from the text.