This government is acknowledged by all, to be one of enumerated powers. . . . But the question respecting the extent of the powers actually granted, is perpetually arising, and will probably continue to arise, so long as our system shall exist. In discussing these questions, the conflicting powers of the general and state governments must be brought into view, and the supremacy of their respective laws, when they are in opposition, must be settled.
If any one proposition could command the universal assent of mankind, we might expect it would be this—that the government of the Union, though limited in its powers, is supreme within its sphere of action. . . . [T]his question is not left to mere reason: the people have, in express terms, decided it, by saying, ‘this constitution, and the laws of the United States, which shall be made in pursuance thereof,’ ‘shall be the supreme law of the land,’ . . .
Among the enumerated powers, we do not find that of establishing a bank or creating a corporation. But there is no phrase in the instrument which, like the articles of confederation, excludes incidental or implied powers; and which requires that everything granted shall be expressly and minutely described. . . .
A constitution, to contain an accurate detail of all the subdivisions of which its great powers will admit, and of all the means by which they may be carried into execution, would partake of the prolixity of a legal code, and could scarcely be embraced by the human mind. . . . In considering this question, then, we must never forget that it is a constitution we are expounding. . . .
The power of creating a corporation, though appertaining to sovereignty, is not, like the power of making war, or levying taxes, or of regulating commerce, a great substantive and independent power, which cannot be implied as incidental to other powers, or used as a means of executing them. It is never the end for which other powers are exercised, but a means by which other objects are accomplished. . . .
But the constitution of the United States has not left the right of congress to employ the necessary means, for the execution of the powers conferred on the government, to general reasoning. To its enumeration of powers is added, that of making ‘all laws which shall be necessary and proper, for carrying into execution the foregoing powers, and all other powers vested by this constitution, in the government of the United States, or in any department thereof.’ . . .
This provision is made in a constitution, intended to endure for ages to come, and consequently, to be adapted to the various crises of human affairs. To have prescribed the means by which government should, in all future time, execute its powers, would have been to change, entirely, the character of the instrument, and give it the properties of a legal code. It would have been an unwise attempt to provide, by immutable rules, for exigencies which, if foreseen at all, must have been seen dimly, and which can be best provided for as they occur. . . .
[T]he sound construction of the constitution must allow to the national legislature that discretion, with respect to the means by which the powers it confers are to be carried into execution, which will enable that body to perform the high duties assigned to it, in the manner most beneficial to the people. Let the end be legitimate, let it be within the scope of the constitution, and all means which are appropriate, which are plainly adapted to that end, which are not prohibited, but consist with the letter and spirit of the constitution, are constitutional. . . .
It being the opinion of the court, that the act incorporating the bank is constitutional; and that the power of establishing a branch in the state of Maryland might be properly exercised by the bank itself, we proceed to inquire . . . [w]hether the state of Maryland may, without violating the constitution, tax that branch? . . .
That the power to tax involves the power to destroy; that the power to destroy may defeat and render useless the power to create; that there is a plain repugnance in conferring on one government a power to control the constitutional measures of another, which other, with respect to those very measures, is declared to be supreme over that which exerts the control, are propositions not to be denied. . . .
If the states may tax one instrument, employed by the government in the execution of its powers, they may tax any and every other instrument. They may tax the mail; they may tax the mint . . . . This was not intended by the American people. They did not design to make their government dependent on the states. . . .
McCulloch also paved the way for what some call the "administrative state," a form of government that employs an extensive professional class to oversee government, the economy, and society. Essentially, the federal regulators who oversee many aspects of American life, including environmental agencies and labor regulators. Without the McCulloch decision, some of these agencies might not exist. Whether the administrative state is a good thing or not is generally a matter of political opinion. Still, there's no doubt that debate would look very different if the Supreme Court had come to a different conclusion in McCulloch.