What do the words “liberty”, “purchase”, and “security” mean in this quotation?

As best as I can tell:

- liberty: the right to be sovereign and able to defend oneself

- security: safety from having taxes levied

- purchase: the guys being taxed said instead “look, we’ll give you money this one time instead but we don’t want you to have the right to levy taxes”

Okay, I guess that makes sense.