The Greek noun katallage means reconciliation, exchange, or restoration of a broken relationship. It appears only 4 times in the New Testament (Romans 5:11; 11:15; 2 Corinthians 5:18, 19) but carries enormous theological weight as one of Paul's central metaphors for the meaning of Christ's death.
Katallage operates on the assumption that there was enmity between God and humanity that needed to be resolved. Romans 5:10 sets the baseline: 'For if, while we were God's enemies, we were reconciled (katallagesomen) to him through the death of his Son, how much more, having been reconciled, shall we be saved through his life!' This is not polite disagreement but cosmic hostility — the wrath of a holy God toward sinful humanity — removed through Christ's substitutionary atonement. Second Corinthians 5:18–20 is the great reconciliation passage: 'God was reconciling the world to himself in Christ, not counting people's sins against them. And he has committed to us the message of reconciliation... We implore you on Christ's behalf: Be reconciled to God.' Three things are remarkable here: (1) God is the initiator — He reconciles; we do not reconcile God to us. (2) The mechanism is Christ's cross. (3) Christians are ambassadors of this same katallage — the mission of the church is reconciliation ministry.