Lady Macbeth is a very ambitious woman, who is ruthless to the point of killing for power.
Please find below an exerpt that I found very intreging in Stephen Greenblatt's interpretation of Macbeth. Upon a closer reading of Macbeth, I have come to understand what Greenblatt describes as poetic transformation. Lady Macbeth, in her soliloquy to unsex herself, she describes pouring her "spirits" in Macbeth's ear. I had initially read this as her persuasive words, influencing her husband Macbeth to murder King Duncan. After reading Greenblatt's interpretation, I agree that pouring spirits in thine ear has two meanings, the other, the pouring of poison into someone's ear, to kill them. Check out Stephen Greenblatt's argument below for an elaboration of this poetic transformation:

"An outstanding example of such a poetic transformation of meaning while preserving the "initial verbal elements" (125) is Lady Macbeth's pronouncement: "Hie thee hither, / That I may pour my spirits in thine ear [...]" (1.5.25-6).**8** "The 'spirits,'" says Greenblatt, "she speaks of here are manifestly figurative [...]" (124). But are they? Certainly the vision of murder done by poison poured into someone's ear did not strike Hamlet's father as "figurative",**9** nor did it Claudius. The closeness of the parallel between the murder of Gonzago and Lady Macbeth's doings is, moreover, borne out by Lucianus's words: "With Hecate's ban thrice blasted, thrice infected, / Thy natural magic and dire property / On wholesome life usurps immediately."**10** This pattern of poisoning through the ear which may have been suggested to Shakespeare by Pliny or by reports of the murder of the Duke of Urbino in 1538,**11** haunted him in such a measure that he employed it as an outstanding topos in three of the great tragedies, for Iago also murders in that way: "I'll pour that pestilence into his ear."**12** Instead of "pestilence" Lady Macbeth says "my spirits", and this leads me to Greenblatt's interpretation:
  • The "spirits" she speaks of here are manifestly figurativethey refer to the bold words, the undaunted mettle, and the sexual taunts with which she intends to incite Macbeth to murder Duncanbut, like all of her expressions of will and passion, they strain toward bodily realization, even as they convey a psychic and hence invisible inwardness. That is, there is something uncannily literal about Lady Macbeth's influence on her husband, as if she [page 63] had contrived to inhabit his mindas if, in other words, she had literally poured her spirits in his ear. Conversely, there is something uncannily figurative about the "sightless substance" she invokes, as if the spirit world, the realm of "Fate and metaphysical aid," were only a metaphor for her blind and murderous desires, as if the Weird Sisters were condensations of her own breath. (124-25)"