He was a long-time theologian at the Congregation for the Doctrine of the Faith and one of the strongest advocates for orthodoxy during the long pontificate of John Paul II.

Scheffczyk was a Mariologist of vast scope, and shown in his role as co-editor and major contributor to the Marienlexikon,[5] a work which totals some 4000 pages.

In his article on Mariology at the Second Vatican Council, he asserts that in pursuing the goal of unity among Christians, though this was legitimate, nevertheless Marian beliefs and devotions had been understated by some representatives of the Catholic Church.

In his view this was the case with the final chapter of the Vatican II Dogmatic Constitution Lumen gentium, dealing with the Virgin Mary.

For Scheffczyk, in this Marian chapter: "The coldness and reserve of this document can be explained, as it is openly admitted, by its showing consideration for ecumenical dialogues especially with Protestants.

[6] He regretted, however, that: The decisive fundamental affirmations (on Mary) are compromises, which narrow the richness of the existing faith and open the way to divergent interpretations, such as the accusation that the Council eliminated the Mediatrix teachings.