What does “promote the general welfare” mean?

Here is the preamble to our Constitution:

We the people of the United States, in order to form a more perfect union, establish justice, insure domestic tranquility, provide for the common defense, promote the general welfare, and secure the blessings of liberty to ourselves and our posterity, do ordain and establish this Constitution for the United States of America.

Quoting Warren and Brandeis from this LINK:

Later, there came a recognition of man’s spiritual nature, of his feelings and his intellect. Gradually the scope of these legal rights broadened  …..the right to enjoy life, — the right to be let alone; the right to liberty secures the exercise of extensive civil privileges  ….

Quote from this LINK

In United States v. Butler,  Justice Roberts wrote for the Court: “Since the foundation of the Nation sharp differences of opinion have persisted as to the true interpretation of the phrase.   ….   Hamilton  maintained the clause confers a power …..  the power of Congress to authorize expenditure of public moneys for public purposes is not limited by the direct grants of legislative power found in the  Constitution.” Appropriations for subsidies and for an ever-increasing variety of “internal improvements” constructed by the Federal Government, had their beginnings in the administrations of Washington and Jefferson.

In United States v. Gettysburg Electric Ry., the Court invoked “the great power of taxation to be exercised for the common defence and general welfare” to sustain the right of the Federal Government to acquire land within a state for use as a national park.

I don’t understand why Congress can’t pass a law making female genital mutilation illegal. What do you think?  Quote from the New York Times article at this LINK :

“As laudable as the prohibition of a particular type of abuse of girls may be,” the judge wrote, prosecutors failed to show that the federal government had the authority to bring the charges, and he noted that regulating practices like this is essentially a state responsibility.  ….. Judge Bernard Friedman of the United States District Court for the Eastern District of Michigan ruled that Congress did not have the authority to pass the law  ….  Shelby Quast said her group, Equality Now, is urging federal prosecutors to appeal the decision. “We are confident that Congress had the authority to pass this FGM law,” she said.