Devarim 32:1

האזינו השמים HEAR YE HEAVENS that I warn Israel, and be ye witnesses to this matter; for so I have told them that ye will be witnesses (cf. Rashi on Deuteronomy 31:28). Similar is the meaning of ותשמע הארץ (i.e. the verb has the force of an imperative: AND LET THE EARTH HEAR). And why did He call heaven and earth as witnesses against them? Moses thought: “I am a being of flesh and blood (mortal); tomorrow I shall be dead. If the Israelites will once say, ‘We have never accepted the covenant’, who can come and refute them?” Therefore he called heaven and earth as witnesses against them — witnesses that endure forever (Sifrei Devarim 306:15). And a further reason was that if they should act worthily, the witnesses might come and give them their reward: the vine might yield its fruit, the ground give its increase, the heaven bestow its dew; while if they should act sinfully, the hand of the witnesses might first be against them (Rashi uses a phrase similar to that used of human witnesses; cf. e.g. Deuteronomy 13:10): “and He will restrain the heaven, that there be no rain, and the earth will not give its increase; and you shall perish quickly” (Deuteronomy 11:17) — through the attacks of other nations (Tanchuma 5:10:1).

Give ear, O heavens, and I will speak; and hear, O earth, the words of my mouth.

הַאֲזִ֥ינוּ הַשָּׁמַ֖יִם וַאֲדַבֵּ֑רָה        וְתִשְׁמַ֥ע הָאָ֖רֶץ אִמְרֵי־פִֽי׃