In his speech, President Roosevelt conveyed the central idea that the United States must establish a government program for providing unemployed people with job opportunities through a number of rhetorical strategies.
First, he used repetition to emphasize the seriousness of the problem of unemployment. He repeated phrases such as "one-third of a nation" and "millions of our citizens" to highlight the scale of the problem and to create a sense of urgency.
Secondly, Roosevelt used vivid imagery to describe the plight of the unemployed, painting a picture of people "living in squalor" and "frozen in the bitter cold." He used this imagery to evoke strong emotions and to create a sense of sympathy and compassion among his listeners.
Thirdly, Roosevelt used rhetorical questions to engage his audience and to challenge their preconceptions. He asked questions such as "why should this nation not be able to do the same thing?" to encourage his listeners to think about what could be done to alleviate the suffering of the unemployed.
Finally, Roosevelt used a call to action to urge his listeners to support his proposed government program. He stated that "there is nothing to fear but fear itself" and that the only thing standing in the way of progress was "inaction." By using a call to action, Roosevelt motivated his listeners to take action and to support the establishment of a government program for providing unemployed people with job opportunities.
Overall, Roosevelt conveyed the central idea that the United States must establish a government program for providing unemployed people with job opportunities through a combination of repetition, vivid imagery, rhetorical questions, and a call to action.