وَإِن مَّا نُرِيَنَّكَ بَعْضَ ٱلَّذِى نَعِدُهُمْ أَوْ نَتَوَفَّيَنَّكَ فَإِنَّمَا عَلَيْكَ ٱلْبَلَٰغُ وَعَلَيْنَا ٱلْحِسَابُ
"Whether We show you part of what We promise them or take you in death: yours is only the delivering of the message; the reckoning is Ours."
And both clauses are built on the same pattern (innamā ʿalayka … wa ʿalaynā) — the division, that is, is shown by the word order as well.
The word balāgh was treated in detail at al-Aḥqāf 46/35, and it was recorded there: the sūra limits its own task to a single word. I rely on that treatment.
And this limit has occurred in many sūras in the index under different words; a table covering seven sūras was set up at al-Qaṣaṣ 28/56 (balāgh, wakīl, jabbār, ḥasarāt, lā yaḥzunka, lā tahdī man aḥbabta, musayṭir). What al-Raʿd adds is this, and it is worth recording: here it is not only the limit that is set down — what lies on the other side of the limit is stated too: wa ʿalayna'l-ḥisāb.
I record this as my own reading: in the others it was said "this is not your task"; here "whose task it is" is stated as well. The place to which the responsibility passes is not left empty.