Against the docetism of the Gnostics, Irenaeus taught that the Incarnation was a true union of God with man, of created with uncreated. Without this ontological basis the soteriological purpose of the Incarnation could not have been made effective. The Incarnation took place in order to recover what was lost in Adam and to complete humanityâs growth to full maturity.16
Full maturity for Irenaeus meant deification â a state always intended but which the Fall had disrupted. It was a spiritual pathway which the Incarnation had restored albeit, according to Mark Edwards, via a different route.17 As Edwards puts it, âthere was therefore a Plan A which was not identical with the one that is now unfoldingâ.18 Not that deification was fully attained in this life exactly â for Irenaeus deification was a journey towards God that the Christian begins at the moment of baptism, but it remains nonetheless a future hope â the fullness of which the Christian looks forward to.19 As Edwards clarifies,
Irenaeus could not say of us that whatever is to be done is done already, but he could say this of Christ, whose eternal ministry has no end any more than it has a beginning, while his ministry on earth is already completeâŚ. At some point in history, God in his plenitude became man, in order that at some unrevealed date in the future man in his fullness may become god.20
This latter point is also one that we find stressed by later Church Fathers, such as Gregory of Nyssa.21
For Russell, the realistic nature of Irenaeusâ account of deification is most clearly evidenced in what has become known as the âformula of exchangeâ (tantum quantum or admirabile commercium), an idea that Irenaeus developed in relation to several scriptural passages, including 2 Corinthians 8.9 and Philippians 2.6â8.22 Irenaeus claims that God became man in order that humans might take on the qualities of Jesus via adoption. This idea appears several times in Irenaeusâ anti-Gnostic writing, Against Heresies (Adversus haereses). For example, in Book Five he states: âOur Lord Jesus Christ, who did, through his transcendent love become what we are, that He might bring us to be even what He is Himselfâ.23 Or as he states in Book Three:
For it was for this end that the Word of God was made man, and he who was the Son of God became the Son of man, that man, having been taken into the Word, and receiving the adoption, might become the son of God.24
In the latter passage, we clearly see Irenaeus linking the idea of exchange to that of adoption. As Russell clarifies quoting Irenaeus, what this entailed was that âthrough the divine sonship a human being is âmingled with the logosâ and becomes a dwelling-place of God (AH 3.19.1; 3.20.2)â.25 Likewise, Fairbairn stresses that for Irenaeus what amounts to deification depends on entering into a relationship with God from which incorruption results. As Fairbairn writes of Irenaeus: âto be united to Christ is to share in his eternal life, his incorruptionâ.26
In contrast to von Harnack who held deification an incursion of Greek philosophy into early Christian thought, Russell stresses that the principle underlying Irenaeusâ exchange formula is biblical.27 As in the early second-century writings of Justin Martyr, Psalm 82.6 acts as a stimulus for Irenaeus.28 In his Against Heresies, Irenaeus cites the verse three times, on each occasion interpreting it in like manner.29 His first usage appears in Against Heresies 3.6.1, and Carl Mosser argues that it seems clear that his opponents had quoted various scriptural verses as evidence that there was a multiplicity of gods â thereby bringing Jesusâ full divinity into question.30 Irenaeus appears to use this verse to counter such a position, stressing that when the Psalmist speaks of âgodsâ, in both verses 6 and 1,31 he does so to indicate that Christians have been adopted as sons and are therefore gods, but only by adoption through grace. They are not gods by nature as Christ is. As Irenaeus states:
He [the Psalmist] refers [in verse 1] to the Father and the Son, and those who have received the adoption; but these are the Church. For she is the synagogue of God, which God â that is, the Son himself â has gathered by himselfâŚ. But of what gods [does he speak in [verse 6]]?⌠To those, no doubt, who...