It is the common fate of the indolent to see their rights become a prey to the active. The condition upon which God hath given liberty to man is eternal vigilance; which condition if he break, servitude is at once the consequence of his crime and the punishment of his guilt.

John Philpot Curran (1750-1817) Irish lawyer and politician

Speech before Privy Council, Dublin (1790-07-10)
    (Source)

On the right of election of the Lord Mayor of Dublin. Commonly paraphrases:

• "Eternal vigilance is the price of liberty."
• "The price of liberty is eternal vigilance."

More discussion (especially regarding attribution to Thomas Jefferson): Eternal vigilance is the price of liberty (Spurious Quotation) | Monticello.