He made further progress through reading first the Church Fathers, especially Tertullian and Irenaeus, and then Tholuck's Lehre von der Sünde, and arrived at unwavering faith in Christ by his fortieth year, realizing that all he sought was to be found in the Lutheran Church, a process begun by the careful study of the Augsburg Confession and its Apology.
Primary collections included all the works of Origen, as well as contemporaries such as Clement of Alexandria, Apollinaris, Justin, Irenaeus, and virtually all the important ecclesiastical writers of the period.
Based on conversation with an unnamed Latin scholar, William Helmcke added that it could also be based on a passage from Irenaeus's Adversus Haereses (Against Heresies): sine initio et sine fine, vere et semper idem et eodem modo se habens solus est Deus ("Without beginning and without end, only God continues truly and always the same and in the same way").
At the end of the summer of 1813 Jean-Claude set off for the major seminary of Saint Irenaeus at Lyon for the final years of preparation for the priesthood.
1 Cor. 15:3 – ο και παρελαβον (I received), omitted by b, Ambrosiaster, Irenaeuslat, Tertullian?