1. "Japan has, therefore, undertaken a surprise offensive extending throughout the Pacific area." - Here Roosevelt uses the word "surprise offensive" wich emphasizes the innocence of the United States. Thay hadn't done anything to Japan, and were attacked by surprise. And by using the word "undertaken" which states that the japanese took the initiative.
2. "Always will we remember the character of the onslaught against us." Here Roosevelt makes sure people don´t forget that this attack was unjustified and very violent. By saying "against us" he wants people to feel angry and to do something against the attackers.
3. "I ask that the Congress declare that since the unprovoked and dastarly attack by Japan on Sunday, December Seventh, 1941, a state of war has existed between the United States and the Japanese Empire." By using "unprovoked" he says again that the United States are not guilty from anything but victims of a treachery. At the same time he uses "dastarly" making the japanese responsable from the attack, making them guilty and without any justification.