So? What does Secretary of the Treasury have to do with Supreme Court lifetime appointments?
After Hamilton retired as Secretary Washington wanted to appoint him to the Court. Since Alexander had eight children he could not afford to take the position though he wanted to.
Like many he had given up a fortune he could have earned working in private practice to work for the federal government (he was the best lawyer in the Country.) So after the years with Washington he had to earn as much as he could.
That quote's point is NOT about just an arbitrary personal relation but QUALIFICATIONS.
Marshall essentially incorporated the Hamiltonian views of the Constitution into the law and compared himself to Hamilton in legal acumen as "a taper to the sun."