At the beginning of Scene 7, Macbeth tries to decide whether to kill Duncan or not. He doesn't think it is a good idea to assassinate Duncan because he thinks "This even-handed justice commends th'ingredience of our poisoned chalice to our own lips" (Line 10-13, Scene 7). Here shows that he realizes justice exists in the world, if he does wicked things, he will definitely be punished by others. Besides, he finds out that Duncan trusts him in two reasons. First, he is Duncan's kinsman and should always protect Duncan; second, Duncan is the guest in his house. Moreover, "this Duncan hath borne his faculties so meek, hath been so clear in his great office" (Line 16-18, Scene 7) here says Duncan is a humble leader, he is free of corruption and his virtuous legacy will speak for him when he dies. Therefore, Macbeth gives up his idea of killing Duncan. I think this monologue has obvious contrast with Macbeth's behavior at the end of this scene which alludes how Lady Macbeth has changed Macbeth.