Apostolic tradition

Irenaeus sees the church as the true guardian of not only the writings but also the teaching and the tradition of the apostles. He illustrates this by indicating the existence of "barbarian" Christians who unable to read the Scriptures, nonetheless hold on to orthodox Christianity. (ch 4) Irenaeus then draws on the tradition to deny heretic speculation regarding the demiurge. (ch 5-6)

Amidst his refutation of the heretics we get a glimpse of Irenaeus' trinitarian theology:

"For the Spirit designates both [of them] by the name, of God—both Him who is anointed as Son, and Him who does anoint, that is, the Father."

And as he refutes the heretics we have the following prayer:

Wherefore I do also call upon thee, Lord God of Abraham, and God of Isaac, and God of
Jacob and Israel, who art the Father of our Lord Jesus Christ, the God who, through the abundance of Thy mercy, hast had a favour towards us, that we should know Thee, who hast made heaven and earth, who rulest over all, who art the only and the true God, above whom there is none other God; grant, by our Lord Jesus Christ, the governing power of the Holy Spirit; give to every reader of this book to know Thee, that Thou art God alone, to be strengthened in Thee, and to avoid every heretical, and godless, and impious doctrine.