Why does it say "Cherev Cherev"?
Rashi, Targum Yonasan: There are two swords ? first of Melech Bavel, and afterwards of Bnei Amon, via the hand of Yishmael ben Nesanyah, who will kill Gedalyah 1 and those who gathered to him from the remnants of the sword.
Radak: This is like people who lament and are pained ? they double their words, like Me'ai Me'ai, Roshi Roshi.
Malbim: The verse depicts that the sword that comes against Yerushalayim, half is sharp in order to slaughter, and half is Merutah, i.e. its blade was removed. Refer to 21:15:5:4.
Radak: Balis Melech Bnei Amon sent him.
What is the significance of "Huchadah"?
Radak: This sword mentioned, that I will remove from its case, it is sharpened to cut well and quickly. The coming verse explains "in order to slaughter."
What is "Merutah"?
Rashi: It is polished.
Rashi citing Menachem: It is removed [from its case].
Radak: The rust was removed so it will be shiny, like polished copper, and scare people.