I think that the relationship between Macbeth and Lady Macbeth is a pivotal part of the play. It is doubtful if Macbeth, who starts off as a brave and valiant warrior, described like "Valour's minion" would have ended up the "Dead Butcher" with his " fiendish Queen", without the driving force of his wife behind him.
Fatally flawed, though his character was, with "Vaulting ambition" Macbeth is basically a good man. His position in society is assured by the noble and brave way he has conducted himself in his service to Duncan the king. The witches prophecies certainly make him stop and think what more could be achieved, but before he has consulted Lady Macbeth, he is still willing to take no action to become king as shown by his thought .
"If chance will have me king, why, chance.
May crown me.
Without my stir".
In his letter to his wife telling her to prepare for Duncan's visit, he confides to her the witches prophecies and refers to her as "My dearest partner of greatness". It is obvious he considers her his equal and confidante and urges her to look forward to his increase in status which she will automatically share with him by becoming Queen.
The audience sees by her reaction to the news, that she knows her husband's character well and is afraid that his basically good nature is "Too full o' the milk of human kindness" for him to commit evil in order to realise his ambitions. She knows he is not above things happening by trickery but does not want to actually employ it himself .
"What thou wouldst highly,.
That wouldst thou holily; wouldst not play false,.
And yet wouldst wrongly win.".
She is determined to use her own spirit to inspire him to get rid of everything in his way. .
When he arrives home, Lady Macbeth has already invoked the spirits of evil to defeminise and dehumanise her,.
"That no compunctious visitings of nature.
Shake my fell purpose,-.
and she greets him with no endearments but speaks to him in a determined tone and forces him to see himself in terms of her plan for power.