What is the meaning of the lines recited by V prior to saving Evey from fingermen?

What is the meaning of the lines recited by V prior to saving Evey from fingermen?

This is a great question! The lines spoken by V are taken from the first act of Macbeth, when a solider is reporting to the king of Scotland about a battle between his majesty's army and rebel forces.

In the following text, the general of the king's army is Macbeth (and the rebels', Macdonwald).

Doubtful it stood; As two spent swimmers that do cling together And choke their art. The merciless Macdonwald, —
Worthy to be a rebel, — for to that
The multiplying villainies of nature
Do swarm upon him, — from the Western isles
Of kerns and gallowglasses is supplied;
And fortune, on his damned quarrel smiling,
Show'd like a rebel's whore.

But all's too weak;
For brave Macbeth, — well he deserves that name, —
Disdaining fortune, with his brandish'd steel,
Which smok'd with bloody execution,
Like valor's minion,
Carv'd out his passage till he fac'd the slave;
And 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.

As you can clearly see, the lines spoken by V are actually a combination of what the soldier says about both Macbeth and Macdonwald.

Now, the meaning behind this — i.e., why V used descriptions from both hero and enemy when first appearing in the film — is subject to interpretation, with two major uncertainties being:

1. Was V introducing himself with this Macbeth reference, or, simply setting a stage for the fight that's to come in the alley (or even, for the entire film)? and

2. Does V specifically identify with Macbeth, or, should the parallels to Macbeth and V for Vendetta be handled a bit more loosely?

If V did make this statement to introduce himself, then, perhaps, this immediately establishes the nature of V's character for all throughout the film; that being, from one perspective he is seen as a rebel, but in fact, he's fighting for a just cause and for the greater good of the people/country.

And then another possible explanation/connection...

Towards the end of the film when V is in the tunnel with Creedy and his squad, V is shown taking off bloodied steel plate armor, which is similar to how Macbeth is described in the quote. Additionally, V was surrounded by a large number of people and was clearly outnumbered, but still had a smile on, and was a worthy rebel, just like Macdonwald. That being said, V's line at the beginning of the film could have been a foreshadowing of his showdown with Creedy.

And lastly, there's also a possible connection in that, upon the Macbeth line being spoken it was the beginning of the end for V, just as it was for Macbeth (after the soldier reported to the king, Macbeth was promoted, which eventually led to him being corrupted by power and the insecurity of losing the power).

Apart from this I hesitate to offer any further explanation, since such attempts tend to be dependent upon how Macbeth itself is being interpreted, and that's a whole other subject.

Being based on an Alan Moore GN (for me, the best adaption of any of his work), it's full of highbrow and clever details such as that.

Macbeth, Act I, Scene II [The merciless Macdonwald] William Shakespeare, 1564 - 1616 A Sergeant, explaining Macbeth’s courage in battle against the rebel Macdonwald

The merciless Macdonwald— Worthy to be a rebel, for to that The multiplying villanies of nature Do swarm upon him—from the western isles Of kerns and gallowglasses is supplied; And fortune, on his damned quarrel smiling, Show’d like a rebel’s whore: but all’s too weak; For brave Macbeth—well he deserves that name— Disdaining fortune, with his brandish’d steel, Which smoked with bloody execution, Like valour’s minion carved out his passage Till he faced the slave; Which ne’er shook hands, nor bade farewell to him...

TLDR; Macbeth fought through seemingly overwhelming odds and killed the traitor Macdonwald, and helped rescue the King's son, Duncan, V overcame odds and rescued Evey.

V also quotes from Hamlet, Twelfth Night and Richard III, which shows he's a well-read, intelligent man, at odds with the majority of the populace under the Orwellian government.