What is "Ru'ach Hashem"?
Radak: It is a spirit of prophecy.
Malbim: It is a wondrous, Divine spirit of Gevurah, that he will not fear to save a great congregation from many [army] camps. It is a level in Ru'ach ha'Kodesh.
Why will Ru'ach Hashem dwell on Sha'ul there?
Radak (5): (a) Because the Aron is there, and (b) "Asher Sham Netzivei Pelishtim" hints that he will remove them and save Yisrael from them.
What is the grammatical form of "Hisnabisa"?
Radak: This is reflexive; the last letter of the root is Hei.
In what sense will he be a different man?
Radak: You will have additional Ru'ach, of prophecy and authority. The same applies to "Hashem switched for him a different heart" (verse 9).
Malbim: It is both regarding his body and soul.
