What is the meaning of "Ki Bochen"?
Rashi: Other afflictions are a great test. Many were tested via calamities, plague, hunger and wild animals.
Refer to 21:18:2:2.
Radak: He took out this sword to test people. He polished it to make it shine and scare people, so they will repent to the good path, and it was sharpened to cut off people if they will not repent.
Malbim: Why do I command to slap the thigh? This will be the test. When you try to slap the thigh, you will find the destructive sword. I.e. the destroyer is on your thigh ? it is not Nebuchadnetzar's sword outside.
Why does it say "u'Mah Im Gam Shevet Mo'eses Lo Yihyeh"?
Rashi (1): What will be with My son if also this staff that despises [all other staffs ? it is much harsher than them] will come upon him, with other tests? My son will not persist [in the world].
Rashi citing Targum Yonasan: Nevi'im prophesized about them, and they did not repent (i.e. it is already tested that they will not repent) ? what will be their end? Also the tribes of Yehudah and Binyamin will be exiled, and they will not persist with their evil deeds. Rashi ? Shevet Yehudah despises her colleague (Yisrael) and mocks them, and the evil that came upon them. Also [Yehudah] will not persist and not rise!
Rashi (2): Why should I wait? Even if they will come to repent and despise idolatry, it will not last. They will soon return to their evil, like He said to Yirmeyah (8:4) "Im Yashuv Lo Yashuv."
Radak: What will this test be, if also the Shevet of My son it despises to cut, just like it despises all wood. This test (polishing and shining) is in vain. This is a Mashal for the Nevi'im's warning [to repent].
Malbim: Even if Shevet Mo'eses will not be, what will they gain? Even if Nebuchadnetzar's staff, which despises all wood, will not consume them, the sword on their thighs will ? they destroy each other. This can be actively (murder), or via their sins, which destroy the city.
