While the Church fathers throughout the entire patristic era manifested common concern to defend and remain within the shared faith of the Church as handed down by the apostles through the generations since their time, Irenaeus of Lyons and Vincent of Lérins paid special, detailed attention to that unity in the faith. In Against Heresies, Irenaeus asserted that all the churches founded by apostles anywhere in the world had maintained and continued to proclaim the apostles’ message and were united in the faith. In Commonitorium, Vincent asserted that the unity of the faith could be discerned in “what was believed everywhere, always, and by all” (quod ubique, quod semper, quod ab omnibus creditum est).
The Church had experienced much change in its political and social situations and had gone through significant doctrinal controversies in the time between when Irenaeus and Vincent made their assertions. This paper will note but only look in passing at those changes and controversies, using them as background for understanding the respective ways Irenaeus and Vincent, in very different circumstances and historical situatedness, articulate that unity. This paper will serve, thus, to help interpret what Vincent urges about the development of doctrine.