What is the meaning of "Yimaa'asu"?
Rashi: They should despise themselves from worry.
Radak: This is like Yimasesu (melting); the Aleph is in place of the doubled letter (Samech). This is like "va'Yimas Levav ha'Am va'Yhi l'Mayim" (Yehoshua 7:5).
What is the meaning of "Chemo Mayim Yis'halechu Lamo"?
Rashi: They should shed so many tears that it is as if they walk through water - "v'Chol Birkayim Telachnah Mayim" (Yechezkel 21:12).
Seforno: [They will be despised] like water that goes over earth (it becomes muddy).
Malbim: Just like water goes - it does not stick together, and separates into drops, so their gathering should separate.
Why did he discuss drawing arrows?
Rashi: Hashem should draw His arrows, in order that they will be pursued.
Radak: When they draw their bows to shoot arrows, the arrows should be like they were broken (Malbim - the heads were broken off), and they cannot harm me. The bow is their mouth, and the arrows are their evil words - "Darchu Kashtam" (64:4).