2Cor 5:17
"Therefore, if anyone is in Christ, he is a new creation. The old has passed away; behold, the new has come."
Kaine ktisis — new creation: not merely a reform of the old, but a new creation. The believer in Christ participates in the new creation inaugurated by Christ’s resurrection. The 'old things' (ta archaia) — the former status as an enemy of God, life under sin — have passed away.
2Cor 5:18-21
"All this is from God, who through Christ reconciled us to himself and gave us the ministry of reconciliation... As though God were pleading through us, we implore you on behalf of Christ, be reconciled to God."
The ministry of reconciliation (diakonia tes katallages): God initiated reconciliation in Christ; we are ambassadors (presbytereuo) who communicate the offer. Verse 21 is the heart of substitutionary atonement: 'For our sake he made him to be sin who knew no sin, so that in him we might become the righteousness of God.'