Wallace: Longshanks desires peace?
Isabelle: He declares it to me. I swear it. He proposes that you withdraw your attack. In return, he grants you title, estates, and this chest of gold, which I am to pay to you personally.
Wallace: A lordship and titles... Gold... That I should become Judas?
Isabelle: Peace is made in such ways.
Wallace: Slaves are made in such ways!
Isabelle is delivering Longshanks' offer in order to declare peace. Wallace is having none of it.