Two dogmatic constitutions from the First Vatican Council, Dei Filius and Pastor Aeternus, are worth revisiting today. These documents were in part a response to the challenge of liberalism. Although such a retrieval of the wisdom of Dei Filius and Pastor Aeternus is necessary as a means of protecting Christ's revelation, this is not sufficient. The doctrine of Pastor Aeternus should also be developed to make more clear the limits of papal authority.