Any decent swordsman knows how to use both hands
In the name of the Warrior, I charge you to be brave. In the name of the Father, I charge you to be just. In the name of the Mother, I charge you to defend the innocent. Arise, Brienne of Tarth... A knight of the Seven Kingdoms.
I promised to fight for the living. I intend to keep that promise.
Threaten? As in "I'm going to open your lord from balls to brains and see what Starks are made of"?