Therefore, lest we suffer any such thing, we must keep the rule of faith unswervingly. And perform the commandments of God, believing in God and fearing Him, for He is Lord, and loving Him, for He is Father. Action, then, comes by faith, as ‘if you do not believe,’ Isaiah says, ‘you will not understand.’ (Isa. 7:9); and the truth brings about faith, for faith is established upon things truly real, that we may believe what really is, as it is, and believing what really is, as it is, we may always keep our conviction of it firm.

Irenaeus of Lyons, On the Apostolic Preaching, 41.