Since the beginning of Abp Prof. Stanisław Wielgus's learned activity he has been interested in history and philology, a fruit of which was his consequent activity in the field of the history of philosophy, mainly medieval, especially with regard to editing medieval manuscripts.

Initially, he focused on editing Polish medieval manuscripts and published Benedictus Hesse. Quaestionis super octo libros "Physicorum" Aritotelis (Wrocław 1984), the text that was accompanied by a study of Benedict Hesse's Quaestionis super octo libros "Physicorum" Aristotelis. Wstęp do krytycznej edycji [An Introduction to a Critical Edition] (Lublin 1983).

With the course of time, he present the results of his studies on medieval biblical literature in Poland, showing also the specific character of the methods of didactics and writing in that period (Badania nad Biblią w starożytności i średniowieczu [Studies on the Bible in the Ancient Times and the Middle Ages], Lublin 1990; Obca literatura biblijna w średniowiecznej Polsce [Foreign Biblical Literature in Poland], Lublin 1990; Średniowieczna literatura biblijna w języku polskim [Medieval Biblical Literature in the Polish Language], Lublin 1991; Średniowieczna łacińskojęzyczna bilistyka polska [Medieval Latin Biblical Studies in Poland], Lublin 1992).

Moreover, he developed a more general reflection on the Middle Ages in Poland and in Europe, showing how medieval philosophy was inspired by religion (Z badań nad średniowieczem [The Studies on the Middle Ages], Lublin 1995; Z obszarów średniowiecznej myśli islamskiej, żydowskiej i chrześcijańskiej [On the Areas of Islamic, Jewish and Christian Medieval Thought], Płock 2002). He showed almost the highest achievement of the Polish philosophical and legal thought in that period. It was the theory of the so-called law of nations, although it was formulated in the context of Polish and Teutonic conflicts and yet it preceded the modern achievements of the philosophy of natural law (Polska średniowieczna teoria "ius gentium" [The Medieval Polish Doctrine of the Law of Nations], translated by J. Grondelski, Lublin 1996, 1998). His work entitled Marsilius von Inghen, Werk und Wirkung. Akten des zweiten Internationalen Marsilius-von-Inghen-Kongresses (Lublin 1993) is particularly important as it shows the influence of particular European accomplishments on medieval Polish thought. This work was an aftermath of the Congress "Marsilius of Inghen and His Times" (KUL 1991).

To sum up these studies on medieval culture we have to mention his work Zachodnia i polska nauka średniowieczna - encyklopedycznie [An Encyclopaedic Approach to Western and Polish Medieval Science], Płock 2005. Rev. abp Wielgus's was active in the administration of KUL, as its rector, a fruit of which is the two-volume book of his addresses Bogu i Ojczyźnie. Uniwersyteckie przemówienia i listy [To God and Homeland. University Addresses and Letters], (vols. 1-2, Lublin 1996-1999), and then as the bishop of Płock (among others, Dobra jest więcej [There is More Good], Płock 2001; Na skale budujemy nasz świat [We are Building our World upon the Rock], Płock 2002; Ducha nie gaście, proroctwa nie lekceważcie 1 Tes 5:19 [Do not quench the Spirit. Do not despise prophetic utterances], Płock 2004; Mocni w wierze przeciwstawiajcie się złu (1 P 5:9) [Resist (the devil), steadfast in faith], Płock 2005. Abp Stanisław Wielgus conducts classes at the Faculty of Philosophy on the history of philosophy in Poland: a doctoral and an MA seminar and a monographic lecture.