ἀδυνατήσει [1 verse](verb 2nd sg fut ind mid or, more likely, verb 3rd sg fut ind act ) "Shall be impossible" is from adynateo, which means "to be unable to do," "lack strength," and of things, "to be impossible." -- The word translated as "will be impossible" is a verb that means "to be unable to do." It is the negative form of the verb commonly translated as "can," which means  "to be able to do," "to have the power to do."  While the form of the verb could be the second person future, "you are going to be unable to do nothing," this double negative would really mean "you are going to be unable to do anything." It could also be the verb form that matches all the verb forms in the sentence, "it will be unable to do anything," with the "it" referring as it has all through the verse, to the stubborn spirit.