Who is "ha'Nichshal Bahem"?
Rashi: The weakest among them.
Malbim: One who stumbled in sin.
How will he be like David?
Radak: He will be a strong warrior.
Malbim: One who sinned will immediately repent, like David, and Hashem will remove his sin. All will be great Tzadikim!
To whom does "Beis David" refer>
Radak: It refers to Melech ha'Mashi'ach, just like "Shim'u Na Beis David" (Yeshayah 7:13) was said about Achaz ha'Melech.
What is "kEi'lokim"?
Targum Yonasan: K'Ravrevin. Rashi ? they are angels.
Malbim: [Beis David] will be like angels, which cannot sin, for they have no Yetzer ha'Ra.
What do we learn from "k'Mal'ach Hashem Lifneihem"?
Rashi citing Targum Yonasan: They will succeed like an angel of Hashem in front of them.
Radak: Melech ha'Mashi'ach will go in front of them to fight, like an angel.
Malbim: Yisrael will honor Beis David as if they are Hashem's angels and messengers to straighten the nation.