Somewhere Oliver Wendell Holmes, Jr. said a true thing (I cannot now place my hand on it, but I’m certain some reader could supply the exact line), to the effect that it would not be calamitous if the federal judiciary had no power to declare acts of Congress unconstitutional, but that the Union itself would be in jeopardy if it had no such power over the acts of the state governments.
Alexander Hamilton would certainly agree with the second half of that Holmesian observation. In Federalist No. 80, turning to the particulars of the federal courts’ jurisdiction under Article III, he takes up the
obvious consideration that there ought always to be a constitutional method of giving efficacy to constitutional provisions. What for instance would avail restrictions on the authority of the state legislatures, without some constitutional mode of enforcing the observance of them?
In the Constitutional Convention, there had been some discussion of lodging in Congress a power to annul state legislative acts directly. That idea had not survived the debate, but a milder, more indirect–and therefore more effective–way of checking the states emerged by way of the judicial power to hold the states to their obligations under the Constitution. One of the most important legacies of John Marshall’s tenure as chief justice was his successful effort to make good on this promise of the Constitution that the policies of the national government within its proper sphere of authority would not be frustrated by contrary or inconsistent state policy choices, let alone by the deliberate opposition of the states.
This was no more than Marshall acting on a principle stated here in No. 80 by Hamilton, of “the judicial power of a government being co-extensive with its legislative,” which ought in turn to be understood in light of the “just principle that every government ought to possess the means of executing its own provisions by its own authority” (Hamilton’s italics). This was a peculiarly important principle given the political relations established by our form of federalism: “The mere necessity of uniformity in the interpretation of the national laws, decides the question.” The alternative is chaos: “the peace of the WHOLE ought not to be left at the disposal of a PART” (his caps too).
Now you have all you need to know to understand why Article III, section 2 is written the way it is. Amid its apparent jumble of jurisdictional threads, there is a warp of separation of powers, and a woof of federalism.
(For explanation of this recurring feature, see here.)