Does the verse command them to request rain from Hashem?
Rashi: Yes, if they need it.
Radak: It teaches that if they will request, He will hear their prayer and make Chazizim and send rain immediately.
Malbim: This is connected to the previous verse. The youths want only grain and wine, but not gems, so they request only rain.
What are "Chazizim"?
Rashi: Clouds that bring rain.
Radak: They are lightning flashes that precede the noise (thunder). He gives lightning together with the rain - "[ba'Asoso la'Matar Chok] v'Derech la'Chaziz Kolos" (Iyov 28:26).
Why does it specify "Malkosh"?
Radak: This is the last rainfall, in Nisan. Even if they need rain at the end [of winter], He will give to them, and the grass will grow quickly.
Malbim: Even if rain should not fall then based on nature, Hashem will send it via Hashgachah.
Why does it say "u'Mtar Geshem"?
Radak: This is like the Semichus "Admas Afar" (Daniel 12:2) and "mi'Tit ha'Yaven" (Tehilim 40:3). He will give an abundance of rain at that time.
Malbim: Matar is Geshem of Hashgachah - not only for the Rabim, rather, even for one man or one grass that needs.
Why does it say "l'Ish Esev ba'Sadeh"?
Rashi, from Ta'anis 9b: For the sake of one man, and for the sake of one [blade of] grass that needs rain. Radak - Hashem will give to the one man who needs, or the one grass that needs, alone. This is like a certain Chasid 1 said, this patch needs rain, and this one does not need.
Radak: For every one, He gives grass in his field.
Yalkut Shimoni 778 brings so about Rav Daniel bar Rav Ketina. The next day, rain came only on the ones that needed rain.
