She knows that people can read Macbeth's thoughts in his face and urges him to .
"Look like the innocent flower,.
But be the serpent under't.".
What Macbeth lacks in ruthlessness she totally makes up for by being both ruthless and committed to striving for the crown no matter what it takes. Macbeth's hesitation and tendency to speculate is seen by her as a weakness. The will needed to carry out the murder of Duncan has to come from her and she says.
"He that is coming must be provided for Leave all the rest to me." .
She is the one that is prepared to take charge and he trusts her.
Even so Macbeth wrestles with his conscience over killing Duncan. He fears the deed will come back to haunt him and he will be condemned to "deep damnation". He is appreciative of Duncan's good qualities, and feels that everyone will mourn his death and really he has no justification apart from his ambition for killing him. .
Lady Macbeth goads him into changing his mind by accusing him of being a coward and even implies that if he does not kill Duncan then he does not love her, .
" From this time, Such I account thy love.".
The final straw is when she accuses of him of not being man enough to do it. .
"When you durst, then you were a man.".
Lady Macbeth is very clever in touching on the two things which she can rely on to sway his resolve; his love for her and his sense of manliness. Although he is afraid of failure, she will not even consider it, so her part in changing his mind is crucial to his becoming a murderer from then on in the play. I think his love for her overcame his conscience and from now on his 'vaulting ambition ' takes over.
Once he has killed Duncan, Macbeth realises the personal consequences to his own state of mind which neither he or Lady Macbeth have yet considered. He becomes almost hysterical as he tells his wife how he has "Murdered sleep" and shall therefore not sleep any more himself. He feels he cannot pray and has destroyed the natural order of things for which God will never forgive him.
