Why does it say "b'Yad Mevakshei Nafshecha"?
Radak: They will not have mercy on you.
Malbim: Some of Yehudah wanted to Tzidkiyah [to be king]. Nebuchadnetzar exiled [Yehoyachin] to fulfill their desire. They wanted to kill him; he feared them. He will be given into their hands, and Nebuchadnetzar's, and the Bavliyim.
Why does it say "b'Yad" four times?
Radak: It is to strengthen the matter. The same applies to "Asher Hitzil Eschem mi'Yad Mitzrayim mi'Yad Pharaoh Asher Hitzil Es ha'Am mi'Tachas Yad Mitzrayim" (Shemos 18:10).
Why will you fear them?
Radak: You will not have strength to stand against them.
Malbim: Refer to 22:25:1:2.
Why does it mention Nebuchadnetzar?
Radak: He is a fierce king - "Alav Alah Aryeh mi'Subecho u'Mashchis Goyim Nasa [Yatza] mi'Mekomo" (4:7).
Why does it mention the Bavliyim?
Radak: They are a fierce, difficult nation that will not show favor "ha'Goy ha'Mar veha'Nimhar" (Chabakuk 1:6).