Kennedy makes a brief allusion to the Roman saying "civis Romanus sum" (3) as justification for his speaking in German when he says that he, too, is a Berliner. From that point on his most important ideas are punctuated with German.

First he uses "Lass' sic nach Berlin kommen" (13) to stress that anyone who doubts that communism is terrible should come see Berlin for themselves. And he ends with a repetition of "Ich bin ein Berliner!" (26) to stress his theme that all people are connected.

These are basically his applause lines. Politicians need those. By breaking into German, Kennedy is making sure that everybody is still listening—and still understanding—and that they're going to cheer for him.