Answer :
In making the statement to Americans during the Great Depression, FDR likely sought to motivate Americans and inspire them to be optimistic in a time of great distress. The statement that the only thing to fear is fear itself basically argues that there is nothing to fear in this world except the act of fearing. At this time many people were fearful for their ability to live and find work and FDR sought to inspire them not to fear and instead to be optimistic and get back to work when the opportunity presented itself for them to do so.