In Act IV, Scene III, Macduff and Malcolm are discussing the qualities that make a good king. Malcom is pretending that he would make a bad king, even worse than Macbeth, he tells Macduff. Malcolm is testing to see whether Macduff is loyal to Scotland. Malcom tells Macduff that he does not possess the “king becoming graces” of justice, verity, temperance, stableness, bounty, perseverance, mercy and lowliness.
A good king would reward his underlings for their merits and loyalty. Macbeth does none of this, and yet he was rewarded by the murdered king Duncan because he was made thane of Cawdor right after an important victory. This was not enough for Macbeth, however, and his ambition, spurred on by the witches’ prophecy, turned him into a bloody tyrant. Macbeth is an unjust ruler and possesses none of the “king becoming graces”. His ambition turns him into a leader that must kill all of those that threaten him; hence he earns his title of “bloody tyrant.”
The morals of the time would have been Christian morals, which Shakespeare labels “king becoming graces.” The term “grace” itself reflects this morality – grace is unmerited favor, and in Elizabethan times, God’s grace was an important aspect of salvation because man did not deserve salvation, but God, in his grace, chose to bestow it upon mankind because of his love. So, too, a king should love his subjects. If a king loved his subjects, he would show them stability, bounty, mercy. Macbeth has none of these qualities, but the murdered king, Duncan did, and certainly Malcolm does as well.