Why does the Sefer begin with "Divrei"?
Radak: This Sefer includes prophecies for Yisrael and for Nochrim, and also Yirmeyah's own matters, what occurred to him with his prophecy for Yisrael.
Radak citing a Midrash: There are three whose prophecies were rebuke, therefore their prophecies are attributed to themselves - "Divrei Koheles" (Koheles 1:1), "Divrei Amos" (Amos 1:1) and Divrei Yirmeyah. They spoke about themselves, e.g. "Ani Koheles Hayisi Melech" (Koheles 1:12), "Kashar Alecha Amos" (Amos 7:10), "b'Terem Etzarcha va'Beten Yedaticha" (verse 5) and evils that people did to Yirmeyah.
Malbim: This teaches that the Sefer includes many matters - visions, prophecies, stories, rebukes, etc. These first three verses are an overview of the content of the Sefer.
Why was Yirmeyah picked to be the Navi to warn about the Churban?
Rashi: The son of a sinner who fixed her ways - Yirmeyah descends from Rachav the Zonah - should rebuke children of Tzadikim who perverted their ways - Yisrael, who come from proper seed and ruined their deeds.
Who was Chilkiyah?
Radak citing his father: He was Chilkiyah ben Shafan ha'Kohen who found the Sefer Torah in Beis Hashem in the days of Yoshiyah (Melachim II, 22:8). His son Yirmeyah prophesized in Yoshiyah's days. His first Nevu'ah was the 13th year of Yoshiyah's reign. Yoshiyah and Yehudah had still not repented until the Torah was found in his 18th year.
Malbim: [This teaches about the author of this Sefer. His father] was Kohen Gadol and a Navi. This teaches that Yirmeyah was rich, for it says "ha'Gadol me'Echav" (Vayikra 21:10) - make [the Kohen Gadol] richer than his brothers (all other Kohanim) 1 .
Nedarim 38a: All Nevi'im are rich! Shitah Mekubetzes (38a) - this is lest they need others (which breeds suspicion of flattery, that he withholds or changes his Nevu'ah amidst fear lest he offend his supporters - PF). Chasam Sofer (38a) - it is so commoners will heed his words.
What is the meaning of "Min ha'Kohanim Asher ba'Anasos"?
Radak citing Targum Yonasan: Min Reishei Matras Kahaniya Min Imarkelaya d'Havu bi'Yrushalayim Gavra d'Kabil Achsantei ba'Anasos. (From the head of the Mishmar of Kohanim, from the overseers that were in Yerushalayim, a man who received an inheritance in Anasos.)
What is "Anasos b'Eretz Binyamin "?
Radak: It is one of the cities of Kohanim, like it says in Yehoshua (21:18).
Malbim: (This teaches about the author's place.) Anasos is a place special for Yir'as Hashem. Yirmeyah was not a resident of Yerushalayim. If a rebuker is from a different city, he does not show favoritism or overlook [sins] amidst love of his birthplace, and his words are heard better.
