1)
Having already written in Pasuk "Vekamta ve'Alisa el ha'Makom asher Yivchar ... ", why does it repeat it here?
1.
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.
2.
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 - which explains why, forty years before the Churban Beis-Hamikdash, they moved to 'Chanus,' 1 when they saw that there were so many murders taking place that they were no longer able to rule according to Din Torah. 2
