What is "Ma'ale ha'Zeisim"?
Rashi: It is Har ha'Zeisim.
Radak: It is the ascent of Har ha'Zeisim.
What is the meaning of "Chafuy"?
Rashi: He was wrapped, like a mourner.
Why was David acting like a mourner?
Malbim: He separated from the Aron, and going on Har ha'Zeisim was separating Ir Hashem (Yerushalayim).
QUESTIONS ON RASHI
Rashi writes that "Ma'ale ha'Zeisim" is Har ha'Zeisim. Why did he go there?
Radak: He went to bow to Hashem, for from there one can see the place of the Mikdash. Even though the Mikdash was not built, and even the place was not known until Gad told him, that it will be built in Aravnah's granary, there was a tradition that it will be on Har ha'Moriyah 1 , just they did not know on which part.
Radak: Some say that from Har ha'Zeisim he could see the tent in which the Aron was.
Zevachim 54b: When David went to Shmuel in Nayos (19:18), they probed where will be the Beis ha'Mikdash. Achitofel was present when David dug the Shisin (conduits through which Neshamos descend from the Mitzvah - Sukah 53a). That was before the rebellion, for Achitofel killed himself (17:23) before David returned to Yerushalayim. If so, David already knew even the place of the Mizbe'ach! (PF)