The theorist, a certain Mr. Rawls, is making a rationalist case that the "best" way to structure society is such that:
I. Each person has an equal claim to a fully adequate scheme of basic rights and liberties, which scheme is compatible with the same scheme for all.In other words, Mr Rawls is specifying a resolution to the "Problem of the Weak". His proposal is a compromise between Marxist views (from each according to their strength, to each according to their need) and Libertarian views (to each according to their strength). Liberalism, in other words.
II. Social and economic inequalities are to satisfy two conditions: first they are to be attached to positions and offices open to all under conditions of fair equality of opportunity; and second, they are to be to the greatest benefit of the least advantaged members of society.
Works for me.