How we cite our quotes: (Paragraph.Sentence)
Quote #1
Furthermore, the people of this country are distant from the troubled areas of the earth and it is hard for them to comprehend the plight and consequent reactions of the long-suffering peoples, and the effect of those reactions on their governments in connection with our efforts to promote peace in the world. (1.4)
The U.S.A. was far away from World War II (except for one point when the Japanese attacked Hawaii, at the time a colonial possession). This is another thing that makes America exceptional: we are guarded from both east and west by oceans and share borders with only two countries, both of whom are allies. This privileged place keeps us safe at home and allows us the time and resources to do stuff like give tons of cash to Europe.
Quote #2
The truth of the matter is that Europe's requirements for the next three or four years of foreign food and other essential products–principally from America–are so much greater than her present ability to pay that she must have substantial additional help, or face economic, social and political deterioration of a very grave character. (4.1)
Marshall namechecks the good old U.S. of A. here, and for good reason. He's talking to Americans and reminding them that all the stuff Europe needs is stuff America has. Again, this is an appeal to the exceptional position America has. This also reminds the listeners that Europe can't repay any loans for quite some time. That's normally not the best negotiating position, and would have been the end of things. But there's that American Exceptionalism. Most countries would want or even need to be paid back in short order. Not the U.S.
Quote #3
It is logical that the United States should do whatever it is able to do to assist in the return of normal economic health in the world, without which there can be no political stability and no assured peace. (6.2)
This is a direct appeal to American Exceptionalism. The U.S. has the ability to help, and therefore must. He takes it as a given that the U.S. should help, noting merely that "it is logical" to do so.