Roosevelt is telling the American public that maintaining an isolationist policy amidst the war will not protect them. All the freedoms that he listed on his speech would be threatened by the march of the Axis powers and it would be a matter of time when they have to confront this threat.
Franklin D. Roosevelt was performing the " Four Freedom" speech through the time of the world war which was a period of suffering between Americans. He is declaring that Americans should not accept that they are totally safe from the war and should be prepared to make certain deductions to defend not only the United States of America but also the foundation of the world. Roosevelt is also making clear that if Germany happens to win the war the American government may fall.
Cassius doesn't want Mark Antony to say anything because he doesn't trust him and he thinks Mark Antony will make matter worse and make them look bad but Brutus allows him to because he believes it will show people that they are not evil and that they did everything in the good interest of Rome.
