What is the function of the emphatic statements Ellison D. Smith uses in his 1924 Congressional Address?

Ellison DuRant Smith was a senator from South Carolina in 1924 when he delivered his anti-immigration speech, often entitled, "Shut the Door."
The speech was an argument in favor of the strict Immigration Act of 1924, also known as the Johnson-Reed Act, which sought to limit the number of immigrants from a particular country to two percent of the total number of people from that nationality in the United States at that time, basing numbers off of an 1890 census. The Johnson-Reed Act was preceded by The Quota Act of 1921, which limited immigrants to three percent of their respective U.S. populations.
These quota laws were passed in response to a great wave of immigration from Southern and Eastern Europe in the late-nineteenth and early-twentieth centuries. These immigrants were seen as undesirables. Meanwhile, immigration from Northern and Western Europe had subsided. Whereas Swedes and Scots had been welcomed, Poles and Italians were eyed with suspicion.
The main fear put forth in Ellison's speech is that the United States would lose its character -- whatever that was at the time -- if it were to allow in too many outsiders. One hears echoes of this rhetoric today, and one has heard it throughout American history. Ellison explicitly states, "I think we have sufficient stock in America now for us to shut the door, Americanize what we have, and save the resources of America for the natural increase of our population." There is fear, too, that newcomers will siphon off resources that "rightfully" belong to native-born whites. 
Race is a key aspect of Smith's speech. He argues for the creation of an American ethnic identity, which was as impossible then as it ever was:

I recognize that there is a dangerous lack of distinction between people of a certain nationality and the breed of the dog. Who is an American? Is he an immigrant from Italy? Is he an immigrant from Germany? If you were to go abroad and some one were to meet you and say, “I met a typical American,” what would flash into your mind as a typical American, the typical representative of that new Nation? Would it be the son of an Italian immigrant, the son of a German immigrant, the son of any of the breeds from the Orient, the son of the denizens of Africa? We must not get our ethnological distinctions mixed up with our anthropological distinctions. It is the breed of the dog in which I am interested. I would like for the Members of the Senate to read that book just recently published by Madison Grant, The Passing of a Great Race. Thank God we have in America perhaps the largest percentage of any country in the world of the pure, unadulterated Anglo-Saxon stock; certainly the greatest of any nation in the Nordic breed.

Smith's emphasis of racial purity and "the Nordic breed" anticipate Nazi rhetoric, which was embraced by some Americans. He is establishing a definition of American identity that is based on northern European heritage -- though, oddly, he does not see Germans, of similar descent, to be a part of that "breed." If America does not "shut the door," he argues, that definition will lose credence. In other words, white supremacy loses credence due to there being no clear understanding of what an American is.
http://historymatters.gmu.edu/d/5080

https://history.state.gov/milestones/1921-1936/immigration-act