In Macbeth, what does conversation between Macduff and Malcolm imply about what audiences would consider acceptable or unacceptable in a king?Act 4.3

This is a great scene and pivotal in understanding both the
characters of Macduff and Malcolm. 

Let us start by understanding
that Malcolm is afraid of returning to England.  He is probably about 14 years old (even though
the movies age him to a ridiculous level) and does not want to go to war against a tyrant.  He
reveals this inital fear through his mistrust of Macduff, whom he cannot believe has left his
family in order to help Malcolm. 

Malcoms
says:

you may deserve
of me through me, and wisdom

to offer up a weak, poor  innocent
lamb

to appease an angry
god.

He is afraid that Macduff is here
to trick him back so Macbeth can kill him.

However, as he grows to
believe Macduff, Malcolm reveals his fears by pretending he is just as bad as Macbeth, that he is
lustful, greedy and ignorant.  Macduff sees through Malcolm's ruse, however, but he is saddened
that he can never return home.

Finally, Malcolm, feeling bad for
Macduff, admits that he does not have what he truly needs to be a
king:

But I have none:
the king-becoming graces,  

As justice, verity, temperance,
stableness,  

Bounty, perseverance, mercy, lowliness,
 

Devotion, patience, courage, fortitude,
 

I have no relish of them, but abound  
 

 In the division of each several
crime,

Acting it many ways. Nay, had I power, I
should

Pour the sweet milk of concord into hell,  
 

Uproar the universal peace,
confound  

All unity on
earth.

This passages reveals
the twelve necessary qualities of a king.  However, Malcolm does not have the confidence to
believe in himself.