Commento su Deuteronomio 28:23

והיו שמיך אשר על ראשך נחשת AND THY HEAVEN WHICH IS OVER THY HEAD SHALL BE COPPER — These curses (i.e. all the curses contained in this chapter) Moses expressed them as though they came from his own mouth (Megillah 31b) whilst those he spoke on Mount Sinai (Leviticus 26), he expressed them as though from the mouth of the Holy One, blessed be He, as indeed is implied by them (by the expressions used), for so it states there: “And if ye will not hearken unto Me”; “And if ye walk contrary to Me”, whilst here it says: “[And if thou wilt not obey] the voice of the Lord thy God”; “The Lord shall make cleave unto thee”; “The Lord shall smite thee”. Moses was milder in his curses, expressing them in the singular (“The Lord shall smite thee”, not “you”, the entire people), and similarly in this curse, too, he was milder, for in the former curses (those in Leviticus) it states, (Leviticus 26:19) “[I will make] your heaven as iron and your earth as copper”, i.e., that the heaven would not exude moisture, just as iron does not exude, and there would therefore be drought in the world, whilst the earth would exude moisture (be humid) just as copper sweats, and it would consequently rot the fruits. Here, however, it states, “Thy heaven shall be copper and thy earth shall be iron”, i.e. that the heavens would exude moisture: even though they might not pour with rain, at any rate there would be no ruinous drought in the world; whilst the earth would not exude moisture just as iron does not sweat, and consequently the fruits would not perish. Nevertheless this is a curse: for whether it (the earth) be as copper or whether it be as iron it will produce no fruit, and the heaven, too, will not pour with rain (give rain in abundance) (cf. Sifra, Bechukotai, Chapter 5 3 on Leviticus 26:19).

והיו שמיך אשר על ראשך נחשת, so that no rain can fall upon the earth from the sky.

These curses Moshe articulated himself, etc. Meaning that Moshe asked the Holy One for permission to curse them this way, and the Holy One granted him permission. This resolves the Gemara's statement (Sanhedrin 99a) that Moshe did not innovate even one letter [in the Torah] on his own i.e., without permission from the Holy One. And when Rashi explains that Moshe “articulated himself,” he means that he first asked the Holy One [for permission]. Tosefos in Chapter Bnei Ha'ir (Megilla 31b), [commenting on the Gemora there] write, “Moshe articulated himself, and through Divine Inspiration.”

V. 23. אשר תחתיך ,על ראשך. Es sind nicht allgemeine Kalamitäten, sie treffen nur dich.

נחושת, “copper;” not literally turning the sky into copper, but delivering moisture only like copper when its “sweats.” The same euphemism is used also for the word ברזל, “iron,” describing the earth beneath. In the commentary by Torat Kohanim, these euphemisms are understood in the reverse sense, i.e. the earth being like copper and the sky like iron. This is the way it had been described in Leviticus 27,19, where the chastisement has been authored by G-d Himself.

יתן ה' את מטר ארצך אבק ועפר, instead, what used to be known as “the rain of your land,” will turn into dust and earth. The wind will act instead as harbinger of rain, as harbinger of clouds of dust, blowing down from the arid and parched earth of the mountains.

It is said, “If you do not heed ‘Me’” etc. But if Moshe pronounced them, it would be impossible to say, “...heed me, etc.”

Still, this is a curse, etc. Rashi is answering the question that if Moshe wanted to curse them, then, what curse is “The heavens above your head will be like copper”?