Meekness is not Weakness
Jesus follows the progression of thought in the intro to his sermon on the mount. First, he talks about being poor in spirit and recognizing our own sinfulness. Next, he talks about mourning over that sin and receiving the comfort of forgiveness. In v. 5 Jesus shows that as a result of that recognition and repentance, we now live a life of meekness and confidence - trusting God to be our defender.