In Act III, Scene I, Banquo warns Macbeth of the consequences of putting too much faith in the witches prophecy, he says in his soliloquy:
Thou hast it now: king, Cawdor, Glamis, all,
As the weird women promised, and, I fear,
Thou play'dst most foully for't: yet it was said
It should not stand in thy posterity,
But that myself should be the root and father
Of many kings. If there come truth from them--
As upon thee, Macbeth, their speeches shine--
Why, by the verities on thee made good,
May they not be my oracles as well,
And set me up in hope? But hush! no more. (III.1)
Banquo chooses the higher moral ground and decides against thinking any further about the prophecy because he sees the temptation in it.
After Banquo's murder, Macbeth has enormous guilt, he begins to see the ghost of Banquo at his party, and is overwhelmed that he is so deeply involved in dangerous murderous treachery and feels surrounded by evil actions. He is suffocating emotionally from the moral strain. In Act III, Scene IV, he says:
By the worst means, the worst. For mine own good,
All causes shall give way: I am in blood
Stepp'd in so far that, should I wade no more,
Returning were as tedious as go o'er:
Strange things I have in head, that will to hand;
Which must be acted ere they may be scann'd. (III.iv)
One moral crisis, and probably the most notable, is the killing of Duncan. From the moment Macbeth is told that he is now the Thane of Cawdor in Act 1, sc. 3, he begins to contemplate being king. He wavers from wanting to kill Duncan to deciding not to do it back to doing it. Lady Macbeth attacks his masculinity when he says "We will proceed no further in this business" in Act 1, sc. 7. Macbeth's reaction to her assault is to go ahead with the murder of Duncan.
Immediately after the murder is Macbeth's next moral crisis, in Act 2, sc. 2. He is immediately struck with guilt. He says he heard voices: "Still it cried 'Sleep no more!' .../... Cawdor/Shall sleep no more; Macbeth shall sleep no more.'" He says he tried, but was unable to say, "Amen": "I could not say 'Amen,'/When they did say 'God bless us!'"
The guilt drips off Macbeth like the blood that drips from the daggers. Another moral crisis occurs at the end of the play in Act 5, sc. 8, when Macbeth meets up with Macduff in battle.
This time Macbeth--still believing himself invincible yet crushed by the blood that calls for blood--tells Macduff that he doesn't want to fight him because he's killed enough of Macduff's family already and because he cannot be killed by any man born of woman.
Macbeth: Of all men else I have avoided thee:
But get thee back; my soul is too much charged
With blood of thine already. (5.8)
Macduff of course gives him the news that he, Macduff, was born by Cesarean birth, "was from his mother's womb/Untimely ripp'd" (Act 5, sc. 8).