The four freedoms described by Franklin Delano Roosevelt in his speech to the seventy-seventh Congress delivered on January 6th, 1941, are succinctly expressed and worth quoting in full:
The first is freedom of speech and expression—everywhere in the world.
The second is freedom of every person to worship God in his own way—everywhere in the world.
The third is freedom from want, which, translated into world terms, means economic understandings which will secure to every nation a healthy peacetime life for its inhabitants—everywhere in the world.
The fourth is freedom from fear, which, translated into world terms, means a world-wide reduction of armaments to such a point and in such a thorough fashion that no nation will be in a position to commit an act of physical aggression against any neighbor—anywhere in the world.
The first three paragraphs of Roosevelt's speech refer to the unprecedented situation in which America found itself in 1941. Every serious threat to the Union, he says, has always come from within (most notably the Civil War). The safety and independence of America had not, since its foundation, been seriously threatened by a foreign power.
The relevance of the fourth freedom is immediately obvious. In order to be free from fear, America must defeat its enemies. The other freedoms refer to the unique conception of America as an exceptional nation set forth in the Constitution, the Declaration of Independence, and the Federalist Papers. Since America aims to be the bastion of the first three freedoms, any attack on the nation is also an attack on that freedom.