From Pope St. John Paul II’s encyclical Fides et Ratio (1984):
Eclecticism is an error of method, but lying hidden within it can also be the claims of historicism. To understand a doctrine from the past correctly, it is necessary to set it within its proper historical and cultural context. The fundamental claim of historicism, however, is that the truth of a philosophy is determined on the basis of its appropriateness to a certain period and a certain historical purpose. At least implicitly, therefore, the enduring validity of truth is denied. What was true in one period, historicists claim, may not be true in another. Thus for them the history of thought becomes little more than an archeological resource useful for illustrating positions once held, but for the most part outmoded and meaningless now. On the contrary, it should not be forgotten that, even if a formulation is bound in some way by time and culture, the truth or the error which it expresses can invariably be identified and evaluated as such despite the distance of space and time.
In theological enquiry, historicism tends to appear for the most part under the guise of “modernism”. Rightly concerned to make theological discourse relevant and understandable to our time, some theologians use only the most recent opinions and philosophical language, ignoring the critical evaluation which ought to be made of them in the light of the tradition. By exchanging relevance for truth, this form of modernism shows itself incapable of satisfying the demands of truth to which theology is called to respond.
— Fides et Ratio 87