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.