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So what meaning does it have?

Pull out your pocket copy of the Constitution, and flip to Article 1 Section 8.

The Congress shall have power to lay and collect taxes, duties, imposts and excises, to pay the debts and provide for the common defense and general welfare of the United States; but all duties, imposts and excises shall be uniform throughout the United States;
....
To make 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 or officer thereof.

In other words, the Federal Government can "provide for the... general welfare of the United States," which would seem to legitimize Social Security and other welfare state programs.