Why does Macbeth express doubt about murdering Duncan in Act I Scene 7?
In his soliloquy at the beginning of Scene 7, Macbeth is vacillating over whether or not to go through with the murder of Duncan. He considers several reasons against killing him. The first is that Duncan is in his house in "double trust," both as his "kinsman" (they are cousins) and his "subject." So to kill him would be to betray that trust in the eyes of God. The second reason is that Duncan has been a good king, admired by his subjects:
Hath borne his faculties so meek, hath been
So clear in his great office, that his virtues
Will plead like angels trumpet-tongued against
The deep damnation of his taking-off.
Finally, Macbeth admits that he really has no reason to kill Duncan other than his own "vaulting ambition," which "spurs" him to the crime. By the end of his soliloquy he has decided not to go through with the murder, at least not in his own castle. It is only the intervention of his wife that changes his mind.
I appriciate the answer of rrteacher (the first answer of this question) and I agree also to the same, But, one thing I would like to add here that ... everyone has intution, which always suggests one what is right and what is wrong.
As for as the intution(voice of soul) of Macbeth is concern, that stopped him in his act of murdering. But one thing more is there, that what is written in your frotune, no one can change that.
And finally, Macbeth is a mirror to show others what would be the result of wrong deeds and Ambition is else but over ambition can destroy you.