I think the comments provided so far give neither proper context or philosophical reference for Cicero's quotation. Considering all of the other works and writings of this greatest of Statesmen, I believe this quote is intended to suggest that liberty is only restrained by the law and that any rational society requires a framework to ensure that liberty does not give way to anarchy. Another way to present this is: The law should ensure the exercise of liberty; otherwise, disperate factions who yield to no authority may arbitrarily infringe one's liberty without recourse. The Law should provide the resourse.