In this scene, Lady Macbeth finally feels a bit of guilt and is finally being moral.

LADY MACBETH

If you get what you want and you’re still not happy, you’ve spent everything and gained nothing. It’s better to be the person who gets murdered than to be the killer and be tormented with anxiety.
Macbeth’s brain status is worsening. Macbeth says that he has burnt a snake but have not killed it. Which indicates how insecure he is, even though he is a king. Macbeth means that he needs to kill Banquo and Fleance, because they both know about the witches’ prophecies and Banquo’s sons are predicted to be kings. Macbeth is not feeling safe because of that. He even says that his ming is full of scorpions because he knows that they are alive.
MACBETH

Oh, full of scorpions is my mind, dear wife!
Thou know’st that Banquo, and his Fleance, lives.
And the most important part is that he is keeping his plan of killing Banquo and Fleance away from his wife. Probably because he is protecting her or because he thinks that he does not trust her.