11 Therefore, the nature of human liberty, however it be considered, whether in individuals or in society, whether in those who command or in those who obey, supposes the necessity of obedience to some supreme and eternal law, which is no other than the authority of God, commanding good and forbidding evil. And, so far from this most just authority of God over men diminishing, or even destroying their liberty, it protects and perfects it, for the real perfection of all creatures is found in the prosecution and attainment of their respective ends; but the supreme end to which human liberty must aspire is God.
Source: Libertas (Vatican.va)