The Catholic faith teaches that grasping the truth about God, His Church, and His moral precepts is not an ongoing process that never ends. The Holy Spirit led the apostles and the Church built on their hand-picked successors “to all truth” (John 16:13).
While it may take some time for the individual to learn and humbly submit to all these truths, these truths have already been revealed and “handed down once for all” (Jude 1:3). The Christian faith was established with certainty and infallibility long before Martin Luther; it cannot be changed, no matter how scrupulously one studies the Bible. Nothing substantive or fundamental can be added to or subtracted from the early deposit of faith.
Personal Scriptural interpretations and younger, man-made Protestant traditions cannot possibly carry greater weight or be more accurate than the Scriptural interpretations of the early Church fathers and councils long before the Protestant Revolution and its “progressive” and innovative doctrinal additions to and subtractions from the one, traditional Faith handed down by the apostles, the foundation of the Church (Eph 2:20).
However, grasping these fixed, traditional Christian truths as they apply to our individual lives and our striving to live out those truths (i.e. sanctification) is indeed an unending, life-long process. We need constant reminders of the truths that have already been revealed to us and constant reflection on how to apply them to our own lives. We need constant prayer for the grace and strength to practice and live out the fixed truths we already know, so that our faith may not be dead, useless, and in vain.
Therefore, Catholicism is distinctly conservative while all other denominations, to a greater or lesser extent, are necessarily liberal, relativist, fallibilist, and egocentric.
Though he’s talking about politics and conservatism, the following quote by William F. Buckley, Jr. (himself a Catholic) in Up from Liberalism applies very similarly to religion and Catholicism:
Conservatives do not deny the existence of undiscovered truths, but they make a critical assumption, which is that those truths that have already been apprehended are more important to cultivate than those undisclosed ones close to the liberal grasp only in the sense that the fruit was close to Tantalus…. Conservatism is the tacit acknowledgement that all that is finally important in human experience is behind us; that the crucial explorations have been undertaken, and that it is given to man to know what are the great truths that emerged from them. Whatever is to come cannot outweigh the importance to man of what has gone before.
With regard to epistemology, i.e. “critical assumption[s],” Protestantism and modern American liberalism are two sides of the same coin.
Conservative Colloquium 