What is the consequence of their evil coming in front of Hashem?
Rashi: They will be punished for their sins.
Ibn Ezra: Do to them for their evil like they did to me for my sins.
Ri Kara: Do not erase their sins.
Palgei Mayim: Those who are not prepared for "Likro Kulam b'Shem Hashem Le'avdo Shechem Echad" (Tzefanyah 3:9, should be punished for their evil.)
What is the meaning of "v'Olal Lamo Ka'asher Olalta Li"?
Rav Sadya Gaon: Strike them like they struck me.
Rashi, Ibn Ezra #1: Do to them [like they did to me]. Olal is like "Gam b'Ma'alalav Yisnaker" (Mishlei 20:11).
Ibn Ezra #2: Olal is a cause, like "v'Lo Niskenu Alilos" (Shmuel I, 2:3).
Ri Kara: Just like You pained me unlike any pain - "Im Yesh Mach'ov k'Mach'ovi" (12), so pain them greatly, unlike any pain.
R. Avigdor: Be meticulous with them like You were meticulous with me.
Palgei Mayim: It uses an expression of Olal, and not Po'el, for Po'el applies to the purpose of the act. Olal refers to the causes that bring the purpose. This is why Hashem is called Ilas Kol ha'Ilos. There is a good purpose for all our afflictions. Therefore we request only that the causes sent on us be sent on them (but not the purpose).
Why does it say "v'Libi Davai"?
Ibn Ezra: My heart mourns until they will be like me, for also they sinned!
Ri Kara: Normally, if one limb hurts, the other limbs are not pained so much. When the heart mourns, the entire body mourns. There is no pain like pain of the heart.