Question

How does Kennedy want his audience to respond to this difference

Answer 1

The celebration was not a VICTORY OF PARTY but a CELEBRATION OF FREEDOM.
Unlike in the American Revolution, every celebration was a victory party against their enemies. The Celebration of freedom is a party that everyone is enjoying because of their forebears fought for freedom against the oppressors.
Here is a part of the speech that will signifies the difference and call to action to the men of today:
"The world is very different now. For man holds in his mortal hands the power to abolish all forms of human poverty and all forms of human life. And yet the same revolutionary beliefs for which our forebears fought are still at issue around the globe--the belief that the rights of man come not from the generosity of the state but from the hand of God.