This is a very interesting scene to examine, because in it Malcolm deliberately lies to Macduff so that he can test Macduff's loyalty. In his speech, Malcolm makes himself out to be a worse tyrant than Macbeth, deliberately lying to exaggerate his vices and lusts:
When I shall tread upon the tyrant's head,
Or wear it on my sword, yet my poor country
Shall have more vices than it had before,
More suffer, and more sundry ways than ever,
By him that shall succeed.
It is when Macduff says that such a king should die instead of being able to live that Malcolm knows that he has a nobleman who is loyal to Scotland above and beyond any particular king. However, it is interesting to consider what this reveals about Malcolm. We see him (needlessly?) lying to one of his followers, that has abandoned his family in Scotland to come and join him, and yet he feels the need to deliberately lie and manipulate Macduff for his own ends and purposes. This shows to my mind that Malcolm actually has the potential to become another Macbeth, abusing and manipulating those under him to suit his personal and private agenda.
Malcolm lies to Macbeth to test his loyalties to Scotland. Malcolm lies about his own weaknesses, claiming that he is more blasphemous than Macbeth. He deceitfully shares his lust and greed with Macduff to taint his own image as a man who is not fit to rule Scotland.
At first, Macduff lightly discards this information about Malcolm's lust and greed. When Malcolm finally convinces Macduff that he is not fit to rule Scotland, Macduff cries out for his homeland:MACDUFF:O Scotland, Scotland!
In the next sentence, Malcolm retracts his lies:
MALCOLM:If such a one be fit to govern, speak.
I am as I have spoken.(115)
Again, Malcolm retracts all his lies, stating that he was testing Macduff's loyalty to Scotland. Macduff passes the test and Malcolm is ready to take on Macbeth. After hearing that his family has been killed by the vicious Macbeth, Macduff is readier than ever to rid Scotland of the evil Macbeth.
Malcolm states his true character and claims his own innocence, proving he would be a good leader:MALCOLM:Macduff, this noble passion,
Child of integrity, hath from my soul(130)
Wiped the black scruples, reconciled my thoughts
To thy good truth and honor. Devilish Macbeth
By many of these trains, hath sought to win me
Into his power, and modest wisdom plucks me
From over-credulous haste. But God above(135)
Deal between thee and me! For even now
I put myself to thy direction and
Unspeak mine own detraction; here abjure
The taints and blames I laid upon myself,
For strangers to my nature. I am yet(140)
Unknown to woman, never was forsworn,
Scarcely have coveted what was mine own,
At no time broke my faith, would not betray
The devil to his fellow, and delight
No less in truth than life. My first false speaking(145)
Was this upon myself. What I am truly,
Is thine and my poor country's to command:
Whither indeed, before thy here-approach,
Old Siward, with ten thousand warlike men,
Already at a point, was setting forth.(150)
Now we'll together, and the chance of goodness
Be like our warranted quarrel! Why are you silent?