How we cite our quotes: (Section.Subsection.Paragraph) or (Section.Paragraph)
Quote #4
The President's counsel, as we have noted, reads the Constitution as providing an absolute privilege of confidentiality for all Presidential communications. (IV.A.2)
This is the Court reiterating Nixon's claim to absolute privilege of confidentiality. We just know this argument's going down.
Quote #5
If a President concludes that compliance with a subpoena would be injurious to the public interest he may properly, as was done here, invoke a claim of privilege on the return of the subpoena. (IV.D.1)
The Court isn't at all contesting the fact that the president has the right to challenge a subpoena on the basis of executive privilege. That's just not what was on the menu.
Quote #6
The need for confidentiality even as to idle conversations with associates in which casual reference might be made concerning political leaders within the country or foreign statesmen is too obvious to call for further treatment. (IV.E.3)
Again, the Court wants to convey that it completely understands a president's need to have conversations protected, even casual ones.