In Act V, scene three, Macbeth recounts a prophecy made by the witches: “Fear not, Macbeth; no man that's born of woman
Shall e'er have power upon thee" (6-7). This prophecy empowers Macbeth not to fear Malcolm, because in his logic, "was he not born of woman?" (4) The witches' prophecy has made Macbeth feel invincible.
At hearing the news of the gathering army, Macbeth confirms his lack of fear for what may happen: "This push Will cheer me ever or disseat me now. I have lived long enough." (23-25) He does not fear death or old age, because he is wholly focused on maintaining his hold over the crown. In his words, he has lived long enough, and he is more than willing to face the battle and go down fighting to control the throne. Death or victory are Macbeth's only foreseeable options.