When Churchill first delivered the "Blood, Toil, Tears, and Sweat" speech, the reception was mixed. Members of the Labour Party were pretty supportive, but many members of the Conservative Party weren't so pleased. They were still loyal to Neville Chamberlain, and weren't so happy to listen to his replacement (source). Like Chamberlain, they'd been reluctant to get involved in another world war.

They'd seen a preview screening of Inglourious Basterds and didn't want anything to do with it.

Since then, especially after Churchill became a hero of World War II, the speech has become one of his most famous. In 2003, Time magazine named it as one of the "80 Days that Changed the World"; they saw the successful appeal to the Labour Party as crucial for creating an effective wartime government (source). Which, of course, led to Britain's wartime resolve, which led to eventual U.S involvement, and well… it changed the world.

Winston Churchill is famous for his speeches, as well as his casual quips and his writing in general. The "We will fight on the beaches" speech he gave the next month is probably more well known, but the BTTS speech has the magnitude of the moment on its side. It was the start of Britain's truly active participation in World War II.