As Churchill gets more dramatic and turns on the poetry, he changes his syntax to a style that's much more designed for a speech than the first section of the text.

Why does he repeat certain words or phrases? For the standard reason: emphasis.

For instance, he says Britain's policy is: "to wage war, by sea, land and air, with all our might…to wage war against a monstrous tyranny" (24). Or, the best example, when he talks about Great Britain's goal for the war:

I can answer in one word: victory, victory at all costs, victory in spite of all terror, victory, however long and hard the road may be; for without victory, there is no survival. Let that be realized; no survival for the British Empire, no survival for all that the British Empire has stood for, no survival for the urge and impulse of the ages. (27-28)

See how many times he says "victory" and "survival"? Notice he only uses "to wage war" twice, but "victory" and "survival" are what he wants in his listeners' heads. That's the message he wants the MPs to come away with. The alternatives are terrifying and demoralizing, hardly the spirit in which to go to war.