extremely strong, brave, relentless, and loyal to his king. He also appears bloodthirsty in how he goes after Macdonwald. It is interesting to later contrast how distraught Macbeth is over killing Duncan when he is clearly used to violent and bloody battles.

In this quotation the sergeant is relaying the events of the Norwegian battle. He uses the metaphor of the 'spent swimmers' to explain the closeness of the fight and to add drama to his tale. He gives a lively account with clever use of sibilance and alliteration to engage his willing audience. The speech is also a device to signal to us, the audience, that Macbeth is a courageous and valiant soldier:

'brave Macbeth - well he deserves that name -'

Shakespeare also cleverly foreshadows the violence with which Macbeth can operate as he dispatches his foes with swift brutality

'he faced the slave,
Which ne'er shook hands, nor bade farewell to him,
Till he unseam'd him from the nave to the chaps,
And fix'd his head upon our battlements.'

This quote comes in Act I, Scene 2.  The sergeant is coming to report to to the king about how the battle is going between the Scots and the Norwegians.  His report is what you quote.

What this means is that the outcome of battle was not clear (doubtful) and the armies were all tired out (spent swimmers) and all they could do was cling together without any technique (choke their art).

In the rest of the quote, the sergeant is telling the king that it was Macbeth who saved the day for the Scots with his bravery.

In some respects, Macduff's desire for revenge, as shown by the above lines, arises out of his own overwhelming feelings of guilt. After all, he did abandon his family to the tender mercies of Macbeth, who proceeded to wipe them out. Instead of taking them with him to England, where he joined up with other renegades and anti-Macbeth rebels, Macduff allowed his family to face the music.

In the event, there was a sense of tragic inevitability about their brutal deaths. And though the ultimate responsibility for this outrage lies fairly and squarely with the tyrant Macbeth, Macduff nonetheless bears some moral responsibility for leaving his family in harm's way.

In terms of the prevailing social norms, Macduff did not behave like a "man" in leaving his family behind. Far from defending and protecting his loved ones, he put them in danger. Macduff knows this all too well, which is why he's so determined to take his revenge upon Macbeth. Social expectations demand nothing less from him, both as a man and as an aristocrat.

According to the traditional gender roles of the time, Macduff has already erred in "playing the woman." Now it's time for him to settle accounts with Macbeth.

This is Macduff's monologue in Act IV, scene iii of Macbeth.  Here's what Enotes "Text and Translation" says:

O, I could cry like a woman with my eyes,
And brag with my tongue! But, gentle heavens,
Cut short all pauses in the action. Bring this fiend of Scotland
And myself face to face;
Put him within my sword's length; if he escapes,
Heaven might forgive him too!

In this scene Macduff has learned of his wife and child's slaughter at the hands of Macbeth.  He no doubt blames himself for leaving them in the castle alone and undefended while he is off to England with Malcolm.

Malcolm wants Macduff to act like a man: to get angry at Macbeth and vow passionate revenge ("let grief convert to anger.").  Malcolm baits Macduff: he wants to use Macduff to avenge his father and get back the throne.

But, Macduff--the hero of the play--has an androgynous side.  He says prior to this, "I must feel it as a man."  He must grieve his dead family before focusing on Macbeth.  He cannot feel two emotions equally at once: grief weighs more than anger.

Macduff is saying that he wishes he could grieve like women and cry, but he can't.  He wishes he could brag about revenge like a man, but he can't.  He's caught somewhere in the middle.  In short, he's a complex human being, not a gender stereotype.

After he grieves, he will convert to action.  In time, he will play the role of hero and avenger, and with God's help, he will let his steel do his talking for him.

This line is spoken by Macduff to Malcolm in Act IV, Scene 3.  In these lines, he is basically swearing to kill Macbeth if he possibly can.  He says this because he has just been told that Macbeth has killed Macduff's wife and kids.

He starts by saying that he could just cry and talk about killing Macbeth.  But instead, he is going just going to stop talking and start acting -- he is going to kill him.  He begs God to put Macbeth near him so they can fight.  He seems to be asking forgiveness for this attitude in the last line.

These words are uttered by the sergeant who returns from the battlefield to inform King Duncan of the outcome of the battle between his army and the invading Norwegian army. The sergeant compares the two sides by employing an image of two fatigued swimmers. Each swimmer struggles to prevent himself from drowning. They are both exhausted, and they attempt to defeat each other in order to save themselves from death. The adjective "spent" means that both of them are drained, and their "art" refers to their swimming skills. However, neither of them can prevail, and they are faced with the threat of death. The literary device utilized by Shakespeare in this part of the sergeant's speech is a simile. This is how the sergeant describes the battle and the unpredictability of it until Macbeth arrives. The sergeant then talks about Macbeth's valor and states how he killed the rebel Macdonwald:

Till he unseam'd him from the nave to the chaps,
And fix'd his head upon our battlements.

As a result, Macbeth is promoted.

When Macduff utters these lines, he has just learned of the murder of his wife and children, the victims of Macbeth's wrath and jealousy. He means that he could cry like a woman over his loss and talk big, like a braggart, about his plans to exact revenge. In referring to tears with the word eyes and voice with the word tongue, Macduff employs a poetic device called metonymy. Metonymy is when a thing or a concept is referred to or replaced by the name of something that is closely related to that thing or concept (like White House for president: the orders came directly from the White House).

After this, Macduff employs a device called apostrophe (not to be confused with the punctuation mark); apostrophe is when a speaker addresses a person or thing that is absent as though it were present and could respond. Macduff speaks directly to the "gentle heavens," imploring God, it seems, to bring him face to face with Macbeth so that he can avenge his hapless family.

The literary device most effectively used in this quote is juxtaposition. In this technique two opposing ideas are placed side by side for dramatic effect. In this particular example it is used to indicate Macduff's anger at Macbeth having had his entire family remorselessly murdered. He is sworn to revenge and will stop at nothing to come face to face with Macbeth and exact his vengeance. One needs a closer look at the text to identify the contrast:

O, I could play the woman with mine eyes
And braggart with my tongue! But, gentle heavens,
Cut short all intermission; front to front
Bring thou this fiend of Scotland and myself;
Within my sword's length set him; if he 'scape,
Heaven forgive him too!

In the first part of his rhetoric, Macduff states that he could be soft and gentle as a woman and be overcome with sadness and weep copiously for the death of his family or he could proclaim loudly and openly about how he was going to punish Macbeth for his evil.

The word 'but' introduces the contrast. Instead of doing just this, he wishes that there be no break or pause in time. He wants to immediately confront the fiendish Macbeth and face him, man to man, and thus engage him in direct battle so that he may avenge the cold-blooded murder of those he loved. This is the manly and courageous thing to do, in contrast to just crying and bragging about what he is going to do to Macbeth.

Macduff's resolve is clearly emphasized in this extract. He is determined and has the courage to confront the malignant tyrant and destroy him, as soon as possible.  

Macbeth's getting cold feet about murdering Duncan. So Lady Macbeth tries to stiffen his resolve. The metaphor she uses has been interpreted in many different ways over the years. Clearly, Lady Macbeth wants her husband to be firm and to stick to what she regards as the correct course of action. But what exactly is a "sticking place"? No one knows for sure. Whatever it is, it's a place where something stops and holds fast. And that's precisely what Lady Macbeth wants her husband to do in relation to killing Duncan.

An especially novel and suggestive interpretation of the metaphor argues that Lady Macbeth is using the image of a soldier with his crossbow, who, to quote from an 1869 edition of the scholarly journal Notes & Queries, would have

his crossbow planted at an angle against the ground, screwing its cord by means of a kind of windlass to ‘the sticking-place,’ or catch, by which it will be held at furthest stretch.

This seems as plausible an explanation as any, not least because Macbeth is himself a soldier and so particularly amenable to such a martial metaphor.

In this quote from Act I, Scene VII, Lady Macbeth is trying to rouse Macbeth and encourage him to overcome his nerves as he thinks about murdering King Duncan. To do this, she uses a metaphor that can be interpreted in a number of ways. She may be comparing Macbeth's courage a musical instrument in which the peg must be tightened or wound up until it sticks into place. Conversely, Lady Macbeth might be making a reference to war: specifically, the tightening of a soldier's crossbow before he fires his arrow.

In addition, this metaphor might allude to the act of sexual intercourse. The word "screw," for example, certainly has sexual connotations. So, in this understanding, Lady Macbeth is telling Macbeth to be a man about it; to stop being a coward and kill King Duncan.

Arguably, Lady Macbeth's metaphor is so effective because it works on so many levels. Furthermore, it really is effective: shortly after, Macbeth goes ahead with the murder.

Lady Macbeth is trying to bolster her husband's courage because he is hesitant to kill King Duncan. He asks, "If we should fail?" Her response is a pun because it offers two meanings. She is telling him to focus his attention ("screw your courage") on killing the king by her reference to the "sticking place," the place the knife will enter his body.

"Screw your courage" can also metaphorically mean to anchor his courage as if he were taking a screw or nail to hold it in place; this place can be a "sticking place" because it will hold his courage like a screw will hold something attached by it. "Screw" also means to force or contort something to a distorted shape, the shape his courage needs to stick (knife) Duncan.

Above all, Lady Macbeth does not want her husband to hesitate or question the plan further. Duncan will spend only one night at Inverness; they have only one opportunity to eliminate him. Macbeth must be brave.