What was the purpose of grandfather clauses?

What two arguments is franklin d. roosevelt making in this excerpt from his "four freedoms" speech? four freedoms by franklin d. roosevelt (excerpt) it is true that prior to 1914 the united states often had been disturbed by events in other continents. we had even engaged in two wars with european nations and in a number of undeclared wars in the west indies, in the mediterranean and in the pacific for the maintenance of american rights and for the principles of peaceful commerce. but in no case had a serious threat been raised against our national safety or our continued independence. what i seek to convey is the historic truth that the united states as a nation has at all times maintained clear, definite opposition, to any attempt to lock us in behind an ancient chinese wall while the procession of civilization went past. today, thinking of our children and of their children, we oppose enforced isolation for ourselves or for any other part of the americas. that determination of ours, extending over all these years, was proved, for example, during the quarter century of wars following the french revolution. while the napoleonic struggles did threaten interests of the united states because of the french foothold in the west indies and in louisiana, and while we engaged in the war of 1812 to vindicate our right to peaceful trade, it is nevertheless clear that neither france nor great britain, nor any other nation, was aiming at domination of the whole world. a) americans should hold on to their isolationist tendencies as long as their own interests are not under threat. b) americans have always fought to uphold human rights and correct injustices against them. c) americans have always been peaceful but should be willing to go to war to defend their allies. d) americans should go to war to protect their allies against the germans and assert their world domination. e) americans should continue to maintain their freedom even in the face of world domination.