Whom will Hashem take?
Malbim: The seed from Beis David that will sprout.
How will Hashem take him?
Radak: I will elevate you to a higher level than you were until that day.
Radak citing Targum Yonasan: I will draw you close.
What is the significance of a Chosam?
Rashi: Since it was decreed about his father Yechanyah "Chai Ani... Im Yihyeh Kanyahu ben Yehoyakim... Chosam Al Yad Yemini Ki mi'Sham Etekenka" (Yirmeyahu 22:24), and it says "Kisvu Es ha'Ish ha'Zeh Ariri" (ibid. 30), we learn that his Teshuvah helped him, and Zerubavel was born to him 1 , and he was made like a signet.
Radak: The ring with which they seal letters is called Chosam - "Simeni cha'Chosam Al Libecha" (Shir ha'Shirim 8:6). That ring does not leave his hand during the day or at night. I.e. Hashem's Hashgachah will be constantly on him.
Malbim: He will be the purpose of the creation and its seal, like the seal of Hashem is Emes and lasts forever.
Radak citing Tanchuma Balak 13: Teshuvah is great - it tears a decree. A son was [conceived] from him when he was in jail - the opposite of "ha'Ish ha'Zeh Ariri." Zerubavel was Yechanyah's grandson. I will make him a Chosam - the opposite of "Im Yihyeh... Chosam."
Why does it say "Ki Vecha Vacharti"?
Malbim: I chose David and his seed.
