"When you teach a child writing, you hold its hand while it forms the letters: that is, it forms the letters because you are forming them.  We love and reason because God loves and reasons and holds our hand while we do it.  Now if we had not fallen, that would be all plain sailing.  But unfortunately we now need God's help in order to do something which God, in His own nature, never does at all--to surrender, to suffer, to submit, to die.  Nothing in God's nature corresponds to this process at all.  So that the one road for which we now need God's leadership most of all is a road God, in His own nature, has never walked.  God can share only what He has: this thing, in His own nature, He has not.

"But supposing God became a man--suppose our human nature which can suffer and die was amalgamated with God's nature in one person--then that person could help us.  He could surrender His will, and suffer and die, because He was man; and He could do it perfectly because He was God." Mere Christianity

The theory of the atonement which Lewis presents as the one which has been most helpful to him is that of Irenaeus and is often called the physical theory of the atonement.  Irenaeus was born in Asia Minor sometime between 130 and 140 AD.  As a young man he listened to the teaching of Polycarp, Bishop of Smyrna, who had in turn sat under the teaching of the Apostle John.  Irenaeus went to Gaul, modern day France, where he eventually became the Bishop of the Church at Lyons.

Irenaeus' belief about the work of Christ may be summed up in one sentence: "Because of His measureless love, He became what we are in order to enable us to become what He is."  What we lost in Adam is recovered in Christ.  Human beings have fallen from God's perfect plan through solidarity with the first human, but we can be restored through solidarity with Christ.

Irenaeus' "recapitulation" theory was based on Paul's teaching which summed up the divine purpose as being "to sum up all things in Christ".  Irenaeus believed that Christ comprised the whole of reality in himself, humanity included.  Christ recapitulated in himself the long history of humankind, but with this great difference: he was obedient at all points to his heavenly Father.  Irenaeus' physical theory of the atonement emphasizes Christ's obedient life but also comprises Christ's death:

in obliterating the disobedience of man originally enacted on the tree [of knowledge of good and evil], He became obedient unto death, even the death on the cross, healing the disobedience enacted on the tree by obedience on a tree [the cross].

Irenaeus and Lewis rightly emphasized Jesus Christ as the only perfect penitent person.  As we identify ourselves with Christ through faith and participation in the sacraments of baptism and the Lord's Supper, our sins are applied to Christ's spiritual bank account and paid for on the cross.  At the same time, Christ's obedience is applied to our spiritual bank account and worked out in our lives by the Holy Spirit.

We can give up trusting in the efficacy of our own repentance to save us and trust in the efficacy of Christ's penitence alone.  Rather than trying to form the letters which spell s-a-l-v-a-t-i-o-n ourselves, we need to relax, let go, and let Christ form those letters in us by his Spirit.  If we let Christ do his work in and through us then, as Irenaeus says, the glory of God will be humanity fully alive!

Almighty God, who upheld your servants Irenaeus and C. S. Lewis with strength to maintain the truth with sparkling clarity: Keep us, we pray, steadfast in true faith, trusting in Christ's perfect penitence, that in constancy and peace we may walk in the way that leads to eternal life; through Jesus Christ our Lord, who lives and reigns with you and the Holy Spirit, one God, for ever and ever. Amen.