Please explain this quote from Macbeth: "Doubtful it stood; As two spent swimmers, that do cling together And choke their..our battlements."
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.