Article VI of the Constitution provides for the assumption by the new government of the debts of the United States as it existed under the Articles of Confederation, that the US Constitution, and all laws made from it are the Supreme Law of the Land (the so-called “Supremacy Clause”), and all that officials, whether members of the state legislatures, Congress, judiciary or the Executive have to swear an oath to the Constitution, with the limitation that no religious test can ever be made for holding of public office.
Assumption of Debts
As indicated previously, one of the most vexing problems under the Constitution involved payment of the national debt, most of which was incurred during the Revolutionary War, and the payment of which was made impossible by the lack of a taxing authority in Congress under the Articles of Confederation. The inability of the national government to make full payment on this debt was both an embarrassment and a source of difficulty in securing the new nation a position among the nations of the world, and particularly those, like France, who had assisted the new nation during the war. One of the most important goals of those who supported a stronger national government was to provide for the payment of these debts.
Under international law, it was possible that the debts of the nation might be avoided due to the radical change in form the Constitution would envision. The first clause of Article VI was inserted with the intention of avoiding the inference that this was the case and to assure the creditors of the nation that the new government would pay the debts of the old.  Madison thought the provision declaratory of the intention not to attempt to avoid the debts created under the Articles of Confederation by a legal devise, but to meet the economic obligations of created under the former form of government. 
The Supremacy Clause provides that the laws of the United States, laws enacted by Congress, and valid treaties made according to the process set out in the Constitution are the supreme law of the land, binding on both state and federal officials. Neither other provisions of the Constitution nor any state laws may allow or create a contrary result. Today, Americans take the supremacy of the national government for granted. However, it is important to remember that this was not the case in 1787. The danger at the formation was not of a federal power capable of rendering state sovereignty illusory, but of states that rendered the national sovereignty illusory.
Under the Articles of Confederation, state courts had the power to interpret the Articles of Confederation and any enactments of Congress under the prevailing doctrinal fact that the national government was not supreme, but only the organ of a confederacy of independent states. This meant that the thirteen states could end up with thirteen different interpretations of federal law. The result was chaos.
The framers were creating a form of government in which there would be dual sovereignty: the states supreme with respect to the matters entrusted to their control and the national government supreme as to matters entrusted to its control.
Hamilton defended this dual sovereignty in Federalist 27, saying:
It merits particular attention in this place, that the laws of the Confederacy, as to the ENUMERATED and LEGITIMATE objects of its jurisdiction, will become the SUPREME LAW of the land; to the observance of which all officers, legislative, executive, and judicial, in each State, will be bound by the sanctity of an oath. Thus the legislatures, courts, and magistrates, of the respective members, will be incorporated into the operations of the national government AS FAR AS ITS JUST AND CONSTITUTIONAL AUTHORITY EXTENDS; and will be rendered auxiliary to the enforcement of its laws. 
The phrases put in capital letters gives Hamilton’s view of the situation. The Federal Government’s supremacy extended to its enactment and enforcement of laws pursuant to its “legitimate, enumerated powers.” Federal and state magistrates, legislatures and courts are bound by such enactments as far as the just and constitutional authority extends.
It was not long, however, before the rather narrow boundaries set by Hamilton were extended by the courts. Chief Justice Marshall, speaking for the Court, stated that ‘‘the States have no power, by taxation or otherwise, to retard, impede, burden, or in any manner control, the operations of the constitutional laws enacted by Congress to carry into execution the powers vested in the general government.”  In the court’s view, their decision was “the unavoidable consequence of that supremacy which the Constitution has declared,” a position that the Court has not changed in the intervening period. 
Oaths and Religious Tests
Under the third clause of Article VI, Senators, Representatives, Members of the state legislatures, and all executive and judicial Officers, both of the United States and of the several states, shall be bound by oath to support the Constitution; however, no religious test can be required as a qualification to any office or public. This provision has two distinct features:
- Both state and national officers must take an oath of loyalty to the Constitution.
- While Congress can designate a form for such and oath, no such oath can involve a “religious test.”
From the beginning, it was envisioned that both state and national officers would need to pledge loyalty to the system of government that the Constitution established. As Madison notes in the Federalist Papers, various provisions contained in the Constitution require the cooperation of state officials to bring to fruition, matters such as the election of Senators and Congressman, and electors for the office of President.  While not without controversy, it is clear that, for the national government to be supreme within its sphere of influence, it would be necessary for state officials to support and defend the Constitution as well as faithfully execute their offices where constitutional matters were concerned. The reverse was not felt to be true, because state governments were sovereign already and the functions of the state government were not similarly intertwined.
A bit of history helps one to understand the prohibition on religious tests. The founders were aware that, at various times, religious tests for office had been a feature of British law, used to force compliance with the religious views of a king or queen. These laws were used during the instability surrounding the period from Henry VIII to the Glorious Revolution in such a way that Catholics and Protestants were impacted. The founders wished to avoid the recurrence of this kind of religious persecution on American soil.
By and by large, the success of Article VI is demonstrated by the relative lack of controversy that it has engendered in recent times. The responsibility of the United States government for the debts incurred under the Articles of Confederation is a problem long solved. Today, the greater problem is the seemingly endless amount of debt the federal government incurs.
In the beginning, it was necessary to work out the implications of the Supremacy Clause, for some if not all of the states were impacted by this provision and it was natural that its scope would have to be defined. Today, the greater difficulty might be in defining the limits of the Supremacy Clause, for today the scope of federal power and responsibility is much greater than at the time of adoption of the Constitution. Consistent with the relational and organic position of these blogs, my view is that the Supremacy Clause is not a warrant for the federal government to ignore the sovereign rights of the states. In a state of dual sovereignty, it is the duty of the greater power to not interfere with the lesser powers without due cause.
The oath of office controversy was substantially a controversy that impacted the adoption of the Constitution and the operation of the government in the early years when fidelity to the Constitution could not necessarily be assumed. Today, the greater issue is the effectiveness of oaths in a world in which oaths and moral commitments are often not seen to be binding.
A particular continuing item of importance is the prohibition on religious oaths. Various more liberal members of Congress have from time to time voiced the opinion that Christians, perhaps especially more conservative Christians, should not be able to serve in certain offices. When the religious tests provision was included in the Constitution, the obvious concern was to prevent a dominant group, probably Protestants, from requiring an oath that would prevent minority religious groups, probably Catholics, from holding office. This was a problem that they clearly recognized as a feature of English history to be avoided. Today, what might be called “secularism” functions as a religion for many people, especially among political and economic elites. The religious tests provision provides (or should provide) a barrier against religious discrimination of exactly the kind the founders sought to avoid.
Copyright 2021, G. Christopher Scruggs, All Rights Reserved
 The Federalist Papers Clinton Rossiter ed. (New York, NY: Mentor Books, 1961) No. 43 (Madison), found at 278. All references to the Federalist Papers are to this edition and cited, “Federalist Papers Number, and Author.”
 It is most interesting that Madison believed the debt to be a moral obligation that should not be avoided by recourse to international law. Id.
 Federalist Papers No. 27 (Hamilton)
 McCulloch v. Maryland 17 U.S. 436 (1819).
 Federalist Papers, No.44 (Madison).