Having already written in Pasuk 8 "Vekamta ve'Alisa el ha'Makom asher Yivchar ... ", why does the Torah insert the "min nha'Makom ha'Hu"?
Rashi (in Sotah, 7b): To teach us that a Dayan can only become a Zakein Mamrei at the hand of the Beis-Din of seventy-one, which sits in the Lishkas ha'Gazis.
Avodah Zarah, 8b: To teach us that the location (the fact that the Beis-Din ha'Gadol is sitting in the Lishkas ha'Gazis) is crucial to the mandate permitting Beis-Din to pass the death-sentence. 1
Avodah Zarah, ibid.: Which explains why, forty years before the Churban Beis-Hamikdash, they moved to 'Chanus,' (an area on the Har Habayis. See Torah Temimah, note 52), when they saw that there were so many murders taking place that they were no longer able to rule according to the Din Torah - See Torah Temimah, note 53.
