What is the meaning of "v'Ne'eman"?
Radak: [Ne'eman] is Nif'al in past tense [and the Vov switches this to future tense]. It means, it will endure, like "u'Skativ Yased b'Makom Ne'eman" (Yeshayah 22:23). Also Yonason translates so.
Malbim: It is feasible that Emunah and Chesed would cease - but not here, for I promised it to you forever.
Why did He say "Lefanecha"?
Radak: Just like your throne is established in front of you today, so it will be forever.
Malbim: Because [the Malchus] is called on your name, it is a reward for your virtue - "v'Halach Lefanecha Tzidkecha" (Yeshayah 58:8).
Why did He say that his throne is established forever?
Malbim: Even if your descendants' throne will cease, your throne will not cease. David himself will sit on his throne in the days of Mashi'ach.
