Who were the Yevusi?
Rashi: They were residents of a region in Yerushalayim called Yevusi. They were descendants of Avimelech.
Radak (Yehoshua 15:63): It is not the name of the nation. Rather, they were descendants of a Pelishti, a descendant of Avimelech, named Yevus.
Metzudas David: It is the name of the nation.
Why did they not dispossess the Yevusi there?
Rashi, citing Pirkei d'R. Eliezer 36: They were not allowed, due to Avraham's Shevu'ah 1 to Avimelech. 2
Radak: The fortress was strong, and Hashem caused that Yehudah could not conquer it until David, so it would be called on his name. "Ad ha'Yom ha'Zeh" is when Shmuel wrote this.
Radak (Yehoshua 15:63): The Shevu'ah was written on copper images. David removed them, and afterwards conquered the tower and bought the Yevusi city for Yisrael from Aravna.
Rashi: The Shevu'ah was "Li ul'Nini ul'Nechdi" (Bereishis 21:23); Avimelech's grandson was still alive. (How would they know this? They never asked from the Urim v'Tumim in Yehoshua's lifetime! Perhaps Hashem told Yehoshua. Or, Serach bas Asher had seen him before descending to Egypt, and recognized him (she was still alive in the 40th year in the Midbar - Rashi Bamidbar 26:46). - PF) Radak (Yehoshua 15:63) - in the days of David, no grandson was alive.
This was taught in Yehoshua (15:63), but there it says that Bnei Yehudah could not dispossess them!
Radak: Yerushalayim is between Yehudah and Binyamin.
Malbim (8): Melech Yerushalayim was the first of the five kings to fight against Giv'on. Yisrael killed him. They surely thought to capture his city, like the cities of the [other of the] five kings that they killed. Yehudah fought, for a strip including [part of] Yerushalayim is in Yehudah's border. They could not dispossess the Yevusi there; they remained "Ad ha'Yom ha'Zeh" (Yehoshua 15:63), i.e. until the end of Yehoshua's lifetime; he wrote his Sefer. After Yehoshua died, there was war between them, and they captured it and burned it, to punish them for their rebellion. However, they did not capture the fortress called later Metzudas Tziyon, until the days of David. The Yevusi were also there. Also Binyamin slackened and did not fight them at all to expel them from his portion.
What is the meaning of "Ad ha'Yom ha'Zeh"?
Rashi (Bereishis 22:14): Whenever it says so in Tanach, it is [forever,] whenever someone will read the verse. 1
Radak, Malbim (8): It is until the end of Shmuel's lifetime; he wrote Sefer Shoftim.
Perhaps it is not always forever. It says "va'Yhi Sham (the Aron was in the Mikdash) Ad ha'Yom ha'Zeh" (Divrei ha'Yamim 2 5:9). This is difficult even if "Ad ha'Yom ha'Zeh" means until this verse was written (after the Churban)! Metzudas David explains there, until the Aron was hidden. (PF)
