Who is speaking now?
Radak: Yirmeyah says that Hashem told me, when I was complaining about them, that my end would be good.
What is the meaning of "Sherisicha"?
Rashi according to Menachem: I left you. It is an expression of remainder.
Rashi according to Dunash: It is an expression of permission - "u'Mesharei Kiterin" (Daniel 5:12). This is like "Pitachticha ha'Yom Min ha'Zikim" (40:4; I released you from the fetters). On the day that Hashem established His word, [Nevuzaradan] said so to him, and "if it is good in your eyes, come with me to Bavel." Also Yisrael asked him to pray for them - "Hispalel Ba'adeinu... Ki Nish'arnu Me'at me'Harbeh" (42:2).
Radak: This is like Sherisicha; there is a Chirik under the Sov in place of a Segol. Also "u'Sefotzosichem" (25:34) has a Chirik under the Tov in place of a Segol 1 . (Here, the word should begin) She'er; the Aleph is omitted. The same applies to "Kol Sheris Yisrael" (Divrei ha'Yamim I, 12:39); it is like She'eris. It is your end, what will remain to you from when their evil comes. Also Yonason translates 'your end will be good.'
Malbim: Even though I told you that I will give their remnant to the sword, you are not included.
Perhaps here he calls Tzeirei 'Segol'. There, Radak explicitly said 'Tzeirei' (PF).
Why is Sherisicha written with a Vov, and we pronounce it with a Yud?
Radak: Aleph, Hei, Vov and Yud are interchangeable.
Why did Hashem say "Im Lo"?
Rashi: It is an expression of a Shevu'ah. Radak - this is like "Im Lo Shivisi v'Domamti" (Tehilim 131:2), "Im Lo Ka'asher Dimisi Ken Haysah" (Yeshayah 14:24).
What is the meaning of "Hifgati Vecha v'Es ha'Ra'ah uv'Es Tzarah Es ha'Oyev"?
Rashi #1: The enemy - when evil will come on them, they will come to you to request mercy for them, like Tzidkiyah said to [Yirmeyah] "Derash Na Va'adeinu Es Hashem" (21:2).
Rashi #2: Nevuzaradan will request from you "if it is good in your eyes, come with me to Bavel" (40:4).
Radak #1: At the time of evil of Yisrael and their afflictions, I will cause the enemy, i.e. Nevuzaradan, to ask you to do what is good in your eyes - to stay or to go. Hifgati is Po'el Yotzei (it acts on others); I will cause him to encounter you and ask you what you want to do.
Radak #2: This is making the sword encounter. "Im Lo Sherisicha" applies to the Navi; "Im Lo Hifgati Vecha b'Es Ra'ah" applies to Yisrael. Also according to my first Perush (refer to 15:11:5:3), "Cheilcha v'Otzrosecha" (verse 13) applies to Yisrael.
Malbim: V'Es ha'Ra'ah, i.e. at the time of the Churban, Nevuzaradan will encounter you, that you will go b'Shalom. And later, v'Es Tzarah, after Gedalyah was killed, your Jewish enemies will ask you to pray for them and advise them what to do.
