How we cite our quotes: (Paragraph.Sentence)
Quote #4
The modern system of the division of labor upon which the exchange of products is based is in danger of breaking down. (3.15)
Marshall spends this paragraph talking about the interplay between urban and rural economies. Basically, rural produces food, urban produces manufactured goods. The war made this system break down entirely. So that needs to be fixed.
Quote #5
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)
In a way, Marshall is warning about the consequences of losing not the war, but the peace. Granted, this situation only developed because of the war, and he's pointing out that a failure to do something will result in even more war. The phase "vicious cycle" might come to mind. It did with Marshall too, who used those exact words.