Hamilton therefore touched on many items in summary fashion.
<>Nor however difficult it may be supposed to unite two thirds or three fourths of the State legislatures, in amendments which may affect local interests, can there be any room to apprehend any such difficulty in a union on points which are merely relative to the general liberty or security of the people. We may safely rely on the disposition of the State legislatures to erect barriers against the encroachments of the national authority.<>
I believe he was carefully addressing a major problem with the Articles of Confederation, which were in force when Hamilton wrote #85, and was a major impetus to the 1787 federal convention in Philly, that being Article XIII which required thee consent of all states to amend the rules of the confederacy.
Twice, Rhode Island alone prevented amendments which would have allowed minimal taxation of imports for a period of years to pay down the enormous debts run up during the Revolution. IOW, as Hamilton lamented, Rhode Island's local interests trumped the national interest.
In the sentence before those you quoted, Hamilton wrote: “And of consequence all the declamation about the disinclination to a change vanishes in the air.” NY and VA had not yet ratified the constitution, and Anti-Federalists were making a major fuss over not only an imperfect constitution, but on that would be un-amendable. They were wrong until 1913.
-PJ