How did Yirmeyah know that they will not hand over Tzidkiyah?
Malbim: Hashem showed me that the women will advocate for you that you are not liable for the rebellion, and you will be vindicated. (This is not explicit.) If you refuse to surrender, they will advocate for you, but you will not be vindicated (verses 22-23.) We infer that if you surrender, you will be vindicated, and it will be good for you!
What is the Kol Hashem that Tzidkiyah should heed?
Malbim: It is what follows (the consequences if he refuses to surrender), and the inference from it (refer to 38:20:1:1).
Is "v'Yitev Lecha u'Sechi Nafshecha" one matter?
Malbim: It is two matters - you will live, and it will be good life.
