Power of Taxation

In Section 928 of his Commentaries on the Constitution, Joseph Story has the following to say about Congress's power of taxation enumerated in Article 1, Section 8:

Having thus disposed of the question, what is the true interpretation of the clause, as it stands in the text of the constitution, and ascertained, that the power of taxation, though general, as to the subjects, to which it may be applied, is yet restrictive, as to the purposes, for which it may be exercised; it next becomes matter of inquiry, what were the reasons, for which this power was given, and what were the objections, to which it was deemed liable.