What is "Keren"?
Radak: It is strength and kingship. The same applies to "Atzmi'ach Keren l'Veis Yisrael" (Yechezkel 29:21), "va'Yarem Keren Meshicho" (Shmuel I, 2:10).
Malbim: It is his Gevurah and strength. I will make it sprout, to answer "Ba'avur David Avdecha" (10).
Why does it say Atzmi'ach (future)?
Radak: It refers to Mashi'ach, in the future. Even though [the kingship] will dry, I will make it sprout. And so it says "va'Hakimosi l'David Tzemach Tzedek", "ba'Yamim ha'Hem uva'Es ha'Hi Atzmi'ach l'David Tzemach Tzedakah" (Yirmeyah 23:5, 33:15). It will be in Tziyon - "v'Alu Moshi'im b'Har Tziyon" (Ovadyah 1:21). And it says "ba'Yamim ha'Hem Tivasha Yehudah vi'Yrushalayim Tishkon la'Vetach v'Zeh Asher Yikra Lah Hashem Tzidkenu" (Yirmeyah 33:16).
Why does it say "Arachti Ner li'Mshichi"?
Radak: This is like "Lema'an Heyos Nir l'David Avdi" (Melachim I, 11:36); the king is like a lamp that illuminates for the nation.
Malbim: This corresponds to "Al Tashev Pnei Meshichecha" (10).
