Deuteronomy 32:1

And when the last end of Mosheh the prophet was at hand, that he should be gathered from among the world, he said in his heart: I will not attest against this people with witnesses that taste of death in this world, behold, I attest against them with witnesses which do not taste of death in this world, and whose destination is to be renewed in the world to come. Isaiah the prophet, when he prophesied in the congregation of Israel, attributed hearing to the heavens, and attentiveness to the earth; because (in his case) earth was nearest and heaven more remote: but Mosheh the prophet, when he now prophesied in the congregation of Israel, attributed hearing to the earth, and attentiveness to the heavens; because (in his case) heaven was nearest and earth more remote; for so it is written, Attend, ye heavens, and I will speak; and hear, O earth, thewords of my mouth.

As I have already explained in Sefer Moznayyim, the word listen [Hebrew: ha ɒzinu] comes from the word “ear” [Hebrew: ozen], as if to say, “incline your ear”.

heavens Sa‘adya Gaon, as I have previously indicated [comment on 4: 26], understands this word metonymically, to refer to the angels. Similarly, earth, he says, denotes the people of the earth. Alternately, the reference is to the testimony of the rain, which falls from the heavens, and to the crops, which grow from the earth. In my opinion, however, the point being made here is that these things are permanent. Compare, “Hear, O mountains” [Micah 6: 2]. Compare as well to Joshua’s stone, where the verse says, “for it has heard” [Joshua 24: 27] [cf. comment on 4: 26]. Previously I have suggested that the human soul is a bridge between the spiritual and the corporeal. It understands everything — even the human soul itself — anthropomorphically: Things corporeal it elevates, and things spiritual it brings down to its own level of understanding.

GIVE EAR, YE HEAVENS. By way of the plain meaning of Scripture, the words of Rabbi Abraham ibn Ezra are correct that the Scriptures designate as witnesses all things which exist and endure. Similarly, Hear O ye mountains, the Eternal’s controversy. So also with reference to the stone that Joshua set up [after he made the covenant with the people], for there it is written, for it hath heard [all the words of the Eternal which He spoke unto us]. And by way of the Truth, [the mystic teachings of the Cabala], the reference here is to the first [higher] heavens and earth mentioned in Genesis, for it is they that shall enter the covenant with Israel. Therefore, he states that the heavens should give ear and listen to the conditions, and how he will apply them.

האזינו השמים, to repay Israel in the event they sin deliberately, as mentioned in Deuteronomy 11,17 where G’d had threatened to withhold the rain, i.e. the blessings that originate in heaven.

האזינו השמים ואדברה, “hearken o heavens and I will speak;” Moses, when addressing heaven and earth mentioned the word האזינו, addressing the ears of heavens first, whereas Isaiah when doing so in Isaiah 1,2 mentioned the word שמיעה, hearing first. The reason is that Moses’ primary field of activity was with heaven, he was close to it and did not need to worry about the ability of the heavens to hear him, but needed their attention to his words. Isaiah being closer to earth than to heaven had to proceed in the reverse order, first making sure that witnesses’ ears were open, before worrying about gaining their undivided attention. When someone is close to the one who addresses him, all he needs to do to get the message is turn his ears in the source of the sound’s direction. A person who is far from the speaker needs to insure first that he is heard, before worrying that what he says will be heard and understood. According to Rashi, (in his commentary on Isaiah) the reason for the opposite approaches taken between Moses and Isaiah is that both heaven and earth are witnesses, (compare Deut. 30,19) seeing they will be around as long as any Israelites exist, they had to be addressed as such in similar terms, i.e. both as hearing and hearkening, (paying attention to what they hear) otherwise each could claim that they were only witnesses to part of what had been demanded of them. Rav Hunna, quoting Rav Acha, claims that from the wording it is clear that there are more witnesses in heaven than on earth, seeing that Moses addresses heaven in the plural mode, האזינו, whereas he addresses earth in the singular mode, ותשמע. Isaiah followed the same pattern he had read about in the Torah, i.e. plural mode for heaven, and singular mode for earth.