The study honors the personality of the late Deacon Professor Petru David (1938-2003), holder of the chair of Missionary Guidance and Ecumenism during 1977-2003, presenting his important contribution in the field of studying the "phenomenon of the sects" and of missiology. The study also highlights his concerns regarding ecumenism and his pleading for local ecumenism, as well as his studies regarding the Romanian history, culture and spirituality. The study finally addresses my own memories from the period of university and doctoral studies, thus completing the personality of the one who was a disinterested mentor of many generations of students in theology.