What is the meaning of "Hirbisa ha'Goy"?
Rashi: You made the nation great to all who hear about them, when the nations will hear that a miracle was done for them.
Radak: You elevated Yisrael above their enemies via the fall of Machaneh Ashur.
Malbim: The Navi says to Hashem, You increase the Simchah of Machaneh Ashur via giving to them all kingdoms of the land.
Why is "Lo [Higdalta Simchah]" written with an Aleph, and we pronounce it with a Vov?
Rashi: The pronunciation teaches that You increased Simchah for him, but not for his enemies. The Kesiv teaches that Chizkiyah's Simchah was not complete, for at that time he was told that everything in his house will be taken to Bavel (39:6).
Radak: The pronunciation refers to the nations mentioned (Yisrael). The Kesiv teaches that You increase Simchah for [Yisrael], but not for their enemies; their Simchah You reduced.
Malbim: The pronunciation refers to Yehudah. You doubled their Simchah via saving them from such a powerful nation; this made them famous.
Why does it say "Samchu Lefanecha"?
Radak: In the Beis ha'Mikdash, they gave [to You] praise and thanks, and rejoiced greatly.
What is the comparison to "Simchas ba'Chatzir"?
Targum Yonasan: Like the Simchah of victors in war. Rashi - it is like reaping. Murderers cut necks. The verse used this expression, for the miracle (wiping out Sancheriv's camp) was on the night of reaping the Omer (Nisan 16).
Radak: It is like people normally rejoice at the time of reaping. The Sov at the end of "Simchas" is in place of a Hei, as if it says Simchah. The same applies to "Im Eten Shenas l'Einai" (Tehilim 132:4), "Shif'as Ani Ro'eh" (Melachim II, 9:17) and similar verses.
Malbim: In one way, the Simchah of reaping grain is greater than that of taking spoils in war, for in war, inevitably some of the victors were killed 1 . In another way, the Simchah of taking spoils is greater, for the Simchah of victory is greatest. Here, they did not fight, and no one died, so it was like Simchah of reaping. It was also like Simchah of dividing spoils, for they were victorious; Hashem's angel killed the enemy.
This refers to a natural war. When Hashem fights for Yisrael, we do not expect any deaths, e.g. Keri'as Yam Suf, the war against Midyan
What does "Ka'asher Yagilu b'Chalkam Shalal" refer to?
Rashi: [Yisrael took] the spoils of Egypt in the days of Moshe. Also here, they divided the spoils of Kush and Egypt, and the desires of all nations. When [Melech Ashur] returned from fighting Tirhakah Melech Kush, he came to Yerushalayim with all the storehouses of Kush and Egypt - "Yegi'a Mitzrayim u'Schar Kush u'Seva'im" (45:14). Chizkiyah and his nation took all the spoils.
Radak #1: Like they rejoiced when they divided the spoils of Machaneh Ashur, so they had a great Simchah afterwards when they came to Beis Hashem to praise and thank for the great miracle.
Radak #2: Like people rejoice when they divide spoils, so they rejoiced in front of You 1 . This is like "Sas Anochi Al Imrasecha k'Motzei Shalal Rav" (Tehilim 119:162).
