How did the Mount Moriah become designated as the Temple Mount?
According to the straightforward reading of Sefer Shmuel (II:Chapter 24), King David was directed to that place by Gad, the prophet, who instructed him to build an altar to God that would end the plague from which the people were suffering. The Gemara on today’s daf (=page) offers a much more detailed description of the long-term planning that went into arriving at this decision.
Rava quotes a passage from Shmuel Alef (19:18-19) where we find Shmuel the prophet sitting with David in Nayot in Ramah. This pasuk (=verse) is difficult since Nayot and Ramah are two different places, so Rava interprets this homiletically as meaning that they sat together in Ramah and discussed noyo shel olam – the beauty of the world – i.e., the Temple. It is clear that the Temple was supposed to be among the highest places in Israel, since the commandment to visit the Temple on the pilgrimage holidays states ve-kamta ve-alita – that people must “go up” to the place chosen by God (Devarim 17:8). In order to determine the place that is considered highest, they studied Sefer Yehoshua (Chapter 15) and found that when the borders of the different tribes were discussed, most of them had their borders described with the words ve’alah – and the border rose up – ve-yarad – the border moved down – and ve-ta’ar – the border was drawn. Regarding the tribe of Binyamin, the word ve-yarad does not appear.
Having determined that the Temple Mount would be in the tribe of Binyamin, they considered placing it in Ein Eitam, which is the highest spot – Rashi identifies Ein Eitam as Mei Nafto’ah based on Yehoshua (15:10) – which, according to the Sages, was one of the springs from which water flowed to the Temple. This was rejected because the Sanhedrin was to be situated in the tribe of Yehudah, which was just to the south of Binyamin, but far from Mei Nafto’ah. This led to the decision to establish the Temple on the border between these two tribes (see Devarim 33:12).
Rashi points out that the source for placing the Sanhedrin in the tribe of Yehudah stems from his blessing in SeferBereshit (49:10), where he is promised to serve the role of mehokek, or legislator. The placement of the Sanhedrin near the Temple is derived from Sefer Devarim (17:9) where we learn that a complicated problem is to be brought to thekohanim–levi’im and to the judges. Thus the Temple was arranged so that it was situated in the tribe of Binyamin with the area of the Sanhedrin in Yehudah.