2 Corinthians 5:17 says "Therefore if anyone is in Christ, he is a new creation, the old has gone , the new has come.
Let us think about this. If we are in our natural self, then we are still ourselves. Nothing change . But if we are in Christ, what Christ did will be in us too.
Another example is if we are in church, are we a new creation ? how about if we are just attending or just visiting ?
Let us continue with next verse which is 18,19 All this is from God who reconciled us to himself through Christ and gave us the ministry of reconciliation: that God was reconciling the world to himself in Christ, not counting men's sins against them. And he has committed to us the message of reconciliation
Paul continues We implore you on Christ's behalf:Be reconciled to God.God made him who had no sin to be sin for us, so that in him we might become the righteousness of God.