1)
What do we learn from "Ru'ach Hashem Diber Bi"?
1.
Rashi: Hashem put Ru'ach ha'Kodesh on me, and it 'spoke' in me. Diber applies to every expression of Nevu'ah, e.g. "ha'Rak Ach b'Moshe Diber Hashem ha'Lo Gam Banu Diber", "Adaber Bo" (Bamidbar 12:2,6). This is because the Ru'ach enters the Navi, and speaks in him.
2.
Radak citing Targum Yonasan: David said this with a spirit of Nevu'ah.
3.
Malbim: There are two levels in which Divine spirit rests on a singer. (a) A Divine power arouses him to sing, but he chooses the words with his intellect. (b) Also the words are via Ru'ach Hashem. David said that both of these came from Hashem. Ru'ach Hashem inspired him to speak, and also "Milaso Al Leshoni."
