Ramban, Deuternonomy 32:1

“Give ear, ye heavens” - By way of the plain meaning of Scripture, the words of Rabbi Avraham Ibn Ezra are correct that the Scripture designates as witnesses all things which exist and endure. Similarly- “Hear o ye mountains, the Eternals controversy ” (Micah 6:2). So also with reference to the stone that Yehoshua set up (after he made the covenant with the people) for there it is written: “for it hath heard...” And by way of the Truth (the mystic teachings of the Kabalah) 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. [Translation by Ramban-Commentary on the Torah. Shilo Publishing House]