Shakespeare presents ambition as a corrupting force throughout Macbeth, using the titular character's tragic trajectory to warn his Jacobean audience of the dangers of unchecked desire. At the play's opening, Macbeth is described as 'brave Macbeth', establishing a heroic baseline that makes his moral decline all the more tragic.
The metaphor of 'vaulting ambition' captures Shakespeare's central warning. The equestrian image suggests a rider who, in attempting to mount his horse, overshoots and falls on the other side - a self-defeating overreach. The verb 'vaulting' carries connotations of both athleticism and recklessness, implying that ambition contains the seeds of its own destruction.
Contextually, Shakespeare was writing for King James I, a monarch who survived the Gunpowder Plot and who believed firmly in the divine right of kings. By showing Macbeth's ambition leading to regicide and damnation, Shakespeare reinforces the Jacobean worldview that usurping a divinely-appointed king invites chaos on both a personal and cosmic level.