What do we learn from the Megilah's size?
Eruvin 21a, partially cited in Rashi (1): David, Iyov and Yechezkeil were all overwhelmed by the vastness of Torah. No one specified [the measure] until Zecharyah did - "Megilah Afah Arkah Esrim ba'Amah v'Rachbah Eser ba'Amah." (This refers to Hashem's Amah. "Afah" means folded.) Unfolded, it is 20 by 20 Amos. It was written "Panim v'Achor" (on both sides) - on one side, it would be 40 by 20 Amos 1 "Mi Modad b'Sha'alo Mayim v'Shamayim ba'Zeres Tiken" (the world is like Hashem's Zeres, so it is half of His Amah.) The Torah is [80 times as long and 40 times as wide, i.e.] 3,200 times the size of the world.
Refer to 5:3:2:1 and the note there.
Radak: He saw it leave Ulam ha'Bayis, which was 20 Amos long (tall) and 10 wide in Bayis Rishon, even though Bayis Rishon was destroyed. This is why it says "ha'Yotzeis...; Hotzeisiha" (3-4).
Maharsha 21a: It is four times its apparent size. This corresponds to four levels of expounding Torah - simple meaning, Drashah, allusion, and deep secret.
