a) It explains why we are in the state that we are in (because of the rational agreement of individuals to organize in society for their own self-interest);
b) It is based on the rational self (we are both rational, and can see the rational structure of our entire natural and social world);
c) It legitimates certain practices on the basis of the rights we have as individuals;
d) It is abstract (based on things like rights of humans, equality, etc.)
e) There is a sense of emancipation. If we just get rid of the barriers to individual rights, we will all live happily.