Why did three of the 30 descend?
'Rashi', Radak: They were the leaders of the 30. Malbim ? they were not the three greatest Giborim, rather, the second set of three Giborim, who were less than the first three.
What is the meaning of "meha'Sheloshim Rosh"?
Rashi (Shmuel II, 23:13) citing Targum Yonasan: From the Giborim, the heads of the camps. Radak (ibid.) ? he translated Sheloshim as Shalishim.
Did they descend onto a rock?
Radak: Yes. The place from which they descended was higher than the rock. The same applies to "v'Yaradti Al he'Harim" (Shoftim 11:37), "v'Yered ha'Sela" (Shmuel I, 23:25).
Malbim: They descended from Yerushalayim to the cave and Metzudah where David was, close to Eretz Pelishtim.
Why does it say here "Al ha'Tzur El David El Me'aras Adulam", and in Shmuel II, 23:13, it says "El Me'aras Adulam"?
Radak (Shmuel II, 23:13): There was a tall, strong rock there. It is the Metzudah ? "v'David Az ba'Metzudah" (verse 16). This was when David fled Sha'ul to Me'aras Adulam. About that place it says "Kol Yemei Heyos David ba'Metzudah" (Shmuel I, 22:4).
Malbim (Shmuel II, 23:13): They came to David to help him. This is the war that David fought against Pelishtim at the beginning of his kingship, when he was in the Metzudah and Pelishtim were in Emek Refa'im (Shmuel II, Perek 5).
