you guys are so pathetic man !!!
isnt it simple "sir, finishing this figh" it means you are going to try and kill the last prophet , Truth, and the arbiter will be on the human side and hand over info about thier wepons and stuff like wat weaknesses thier ships have ( if you read the fall of reach chapter 13 i think you will know wat i mean )
also the elites and grunts will be over to our side and even though thay are week agains a brute they are strong in numbers.
Cortana chose to be left behind in the holly city beacuse she knew the gravemind guy would come and she wanted to know more about the 7 rings called halo