“Distinguish legal status from economic resources from social power” — what does “rather than treating them as one thing” mean?

It means don't assume that being equal in one dimension means being equal in all dimensions.

For example:

Legal status

Person A and Person B are both legally free citizens.

Economic resources

Person A:

owns 500 acres and has capital.

Person B:

owns no land and has little capital.

So they have equal legal status, but unequal economic resources.

Social power

Person A:

belongs to the socially dominant racial group and is recognized as socially superior.

Person B:

belongs to a group that has historically been subordinated.

So they may also have unequal social power.

Therefore:

legal equality is not the economic equality and it is not the social equality

They are related, but they are not the same thing.