What is the difference between 'Ha'azanah' and 'Shemi'ah'?
Da'as Zekenim, Hadar Zekenim #1, Rosh, Targum Yonasan: 'Ha'azanah' applies to someone who is close by, and 'Shemi'ah' to one who is far away.
Hadar Zekenim: They are the same. Moshe changed expressions for a nicer wording.
What should the heaven and the earth pay attention and listen to?
Rashi: They should pay attention to the fact that Hashem was warning Yisrael
Why did Moshe call specifically upon heaven and earth to act as witnesses?
Rashi #1: Because, in the event that Yisrael argue that they did not accept the covenant that Hashem made with them, whereas he, being human, will no longer be in the world to rebuff their claims, heaven and earth exist forever and will be able to do so.
Rashi #2 and Rashbam: Because heaven and earth are able (to give Yisrael reward if they merit it
See R. Chavel's footnotes.
Ramban: And it is in this connection that the Torah writes in Pasuk 2 "Ya'arof ka'Matar Likchi" - with regard to written Torah (from the Heaven); "Tizal ka'Tal Imrasi" - with regard to oral Torah (from the earth); and in Pasuk 3 "Ki Shem Hashem Ekra" - with regard to the Heaven; "Havu Godel l'Eilokeinu" - with regard to the earth.
Why did Yeshayah (1:2) reverse the order of Moshe and exclaim "Shim'u Shamayim Veha'azini Eretz!"?
Targum Yonasan, Da'as Zekenim #1, Hadar Zekenim #1, Rosh #1: Refer to 32:1:1:1. Yeshayah, who was closer to the earth than to the heaven, ascribed Ha'azanah to the earth and Shemi'ah to the heaven, whereas Moshe 1 reversed the order because he was closer to the heaven.
Rashi (Yeshayah 1:2), Da'as Zekenim 2 #2, Rosh #2: Witnesses' testimony is valid only if they match. Moshe called to Heaven with Ha'azanah and to the earth with Shemi'ah. They do not match. Therefore, Yeshayah called each with the other expression, so now they were invited to be witnesses with the same expressions.
Hadar Zekenim: Yeshayah switched the expressions to show that they are identical.
Hadar Zekenim: Hashem's honor is in Heaven, and He is closer, therefore
Why does it not say who sang this Shirah, unlike all other Shiros?
Hadar Zekenim and Riva, both citing R. Baruch, and Rosh: There are harsh rebukes of Yisrael, therefore Moshe's name is not explicit, but the initial letters of the first verses hint to Moshe. The Hei, Yud, Chaf and Hei of Ha'azinu, Ya'arof, Ki and ha'Tzur have a [sum] Gematriya of 40, like Mem. The next verses begin with Shin (Shiches) and Hei (Ha la'Shem).