“Everything in the world is purchased by labor.”

From Hume's point of perspective and reference, yes — accurate. Even mass poverty is purchased and expanded by the endeavors (labor) of despots.

In the absence of Virtue, even labor, which was ordained to be inherently honorable, can be rendered ignoble or, at best, a duel edged sword.

Intention, purpose and Values make the defining difference.

Labor is the exercise of Life.  That inherent power is a gift, prized above all -— it is the source of 'value' and 'worth' in the material world.  All value is determined by the effort and the labor required.  But what is the Life of a man/woman worth?  Is the apple in the tree worth the effort to harvest it?  Unless the fruit drops from the tree into my hands, labor will be required.  Systems have been put in place to attempt to 'cheat' these natural laws, but all they have done is put a lien upon the labors of the People perpetually, indebted forever.  The command of labor is the goal of all would-be rulers.

The salvation that Liberty and Freedom provides, is not purchased by the labor of man, but defended. From Hume's perspective as a secular humanist naturalist, he is constrained by a carnal mind. Narrow in scope siding only with that that can be seen. On the surface, the quote seems proper, yet Hume implies a deeper meaning. 

Except, of course, if you're a politician. Then it is taken from the laborer under the guise of a loosely defined  "infrastructure", as though it's the right of the "know better" politician to do so.

Be that as it may, criminal purchasing power is much, much, much more vast then that of honest well meaning law abiding force times distance laboring fellow.