The current inequality is unjust and only occurs because the ones with power pass their privileges to their children.
Rawls came up with the following thought experiment: Suppose we all sit behind a veil of ignorance and have to decide how a just society would look like. That is, we don’t know where our place in the society will be with respect to wealth, health, gender, sexual orientation, ethnicity, etc. According to Rawls we would devise a society with a best worse case scenario, where the ones with the least resources do better than in any other conceivable society.
Such a society can only be achieved if all differences are eliminated as far as possible. The only difference or inequality Rawls considers admissible is due to ability if it increases the well-being of the least fortunate. For him justice is fairness.