Sending "upon": what comes down, and the guardians
Construed with عَلَىٰ, the verb أَرْسَلَ ("to send") describes something coming down upon a target: rain, a wind, a cry, stones. With the same construction, guardians are sent "upon" human beings by God alone; whenever it is a matter of sending the Prophet or human beings as guardians over others, the sentence is negated.
The survey counts 24 occurrences of أَرْسَلَ followed by عَلَىٰ within three words.
Nineteen concern something falling from above: rain (« يُرْسِلِ ٱلسَّمَآءَ عَلَيْكُم مِّدْرَارًۭا », 71:11), the icy wind (54:19), the cry (54:31), the birds and their stones (105:3), the flood and the locusts (7:133). The preposition gives the direction: from above onto the target.
The other five concern guardians, and the division is clear:
- affirmed once only, with God as subject: « وَيُرْسِلُ عَلَيْكُمْ حَفَظَةً », "He sends upon you guardians" (6:61);
- negated four times when it concerns the Prophet (4:80, 17:54, 42:48: « فَمَآ أَرْسَلْنَٰكَ عَلَيْهِمْ حَفِيظًا ») or human beings (83:33: « وَمَآ أُرْسِلُوا۟ عَلَيْهِمْ حَٰفِظِينَ »).
No occurrence departs from this division. The translation renders عَلَىٰ as "upon" throughout.
In the text
يُرْسِلِ ٱلسَّمَآءَ عَلَيْكُم مِّدْرَارًۭاوَأَرْسَلَ عَلَيْهِمْ طَيْرًا أَبَابِيلَوَيُرْسِلُ عَلَيْكُمْ حَفَظَةًفَمَآ أَرْسَلْنَٰكَ عَلَيْهِمْ حَفِيظًاوَمَآ أُرْسِلُوا۟ عَلَيْهِمْ حَٰفِظِينَ