In Shakepeare's Macbeth Act 4.3, news of the slaughter of Macduff's family by Macbeth's soldiers has not yet reached England, so Malcolm doesn't know whether or not he can trust Macduff. Fair is foul and vice-versa in the play, and Malcolm thinks Macduff may be an agent for Macbeth.
To test him, Malcolm puts Macduff through a series of tests, telling him consecutively that he himself is full of lust, greed, and is an all around terrible human being. Macduff explains away the lust and greed, and says Malcolm can still be king with those faults. But Macduff rejects Malcolm after the third test, telling him that he isn't even fit to live.
That's what Malcolm wants to hear. He takes that as proof that Macduff is loyal to Scotland, not to Macbeth. His faith in Macduff is confirmed near the end of the scene when news reaches them that Macduff's family has been slaughtered. Macduff is obviously not on Macbeth's side.
Malcolm and Macduff both put Macbeth's actions into perspective. Macbeth's decisions and actions serve Macbeth's interests. His focus is on gaining power and maintaining it. Malcolm, who actually has the right to the throne since he is Malcolm's heir, focuses on the good of Scotland. He doesn't want someone on his side that would fight for someone to be put on the throne of Scotland, who doesn't deserve to be on the thrown of Scotland. Malcolm has Scotland's best interests on his mind.
In addition to that explained above, Malcolm's speech also outlines what he feels are the characteristics of a strong king. Malcolm says,
"But I have none: the king-becoming graces, as Justice, Verity, Temp'rance, Stableness, Bounty, Perseverance, Mercy, Lowliness, Devotion, Patience, Courage, Fortitude. . ." (IV.iii.91-94).
Malcolm claims that he does not have any of these characteristics, and therefore, would not make a good king. The irony is that Macbeth does not have any of these qualities either. In fact, Macbeth has proven to be quite the opposite of what a good king should be. So even if Malcolm does not feel like he would be a great king, chances are, he would be much better than Macbeth. So, the irony in this part of Malcolm's speech puts Macbeth's actions as king into perspective.
Malcolm is discussing Macbeth's actions (including the murder of Macduff's family) with Macduff. It is important to note that the action of the play has moved from Scotland to England, where Malcolm has been hiding out since the murder of King Duncan, his father.
Malcolm does begin the scene listing all of Macbeth's atrocities and describing the evil elements of his nature, but then he shifts into listing his own sins, his own evils. These are all countered by Macduff as things that would not affect his ability to rule justly as king. Finally, Malcolm admits that these "evil" acts of his own that he has listed are not true acts he has committed and that his only desire to serve his country. He says:
By many of these trains hath sought to win me
Into his power,...but God above
Deal between thee and me. For even now
I put myself to thy direction, and
Unspeak mine own detraction, here abjure
For strangers to my nature....[W]hat I am truly
Is thine and my poor country's to command.
So, he places himself in Macduff's hands and commits himself to the good of Scotland, to serve his people and country as King.
I am not sure either how this exactly puts "Macbeth's actions into perspective," except that though Macbeth's crimes have been many, Malcolm doesn't see him as some sort of devil incarnate, but a man with weaknesses, just as he, Malcolm, has inside him. The only thing that separates them is that Macbeth has acted upon the sinful, evil ideas that have come to him, and Malcolm has refrained.