Macbeth breaks the sacred King-Thane relationship bonds of "Comitatus" when he decides to kill Duncan. More, he and Lady Macbeth commit the most heinous crime in Elizabethan England: regicide. According to James I's belief in the "Divine Right of Kings," Macbeth's act of betrayal is the equivalent of killing God.
Regicide violates the natural order of the universe. It makes the natural world turn unnatural. After Duncan's murder, Macbeth hears, "Macbeth hath murdered sleep." Owls devour falcons. Duncan's horses eat each other. The earth shakes and shrieks of death are heard. Time begins to spin backwards. Foul become fair. Evil reigns.
Macbeth and Lady Macbeth both betray their King, country, God, and nature in committing regicide. Not only that, but regicide is a vile act of domestic terrorism, and there are references to the most infamous act of terrorism of the time, the Gunpowder Plot, all through the play.
Macbeth doesn't stop with Duncan. He kills another Thane (Banquo); tries to kill Banquo's son; kills women (Lady Macduff) and children (her son). His first act of betrayal leads to others: hence, "blood begets blood." He is the antithesis of Duncan, as he conferences with witches and murderers as his advisors.
The two most loyal Thanes are Banquo and Macduff. Banquo serves as the loyal foil to Macbeth's betrayal in Acts I and II. Macduff serves as the most loyal of the remaining Thanes in Acts III through V. Macduff is so loyal to Scotland that he even forsakes his family's safety (leaving his castle unguarded) in order to make ready the preparations of war in England against Macbeth. When he is told of his family's murder, he continues his course of revenge against Macbeth steadily.