"For the laying of taxes is the power, and the general welfare the purpose for which the power is to be exercised. They are not to lay taxes ad libitum for any purpose they please; but only to pay the debts or provide for the welfare of the Union. In like many, they are not to do anything they please to provide for the general welfare, but only to lay taxes for that purpose.
To consider the latter phrase, not as describing the purpose of the first, but as giving a distinct and independent power to do any act they please, which might be for the good of the Union, would render all the preceding and subsequent enumerations of power completely useless."
(Emphasis added to Jefferson quote by Double Birds)
Jefferson quote source: Opinion of the Constitutionality of a National Bank.
