What is the biblical doctrine of reconciliation?
It is the restoration of friendship or fellowship of someone who has been estranged. In our case, it is fallen, sinful humans being resotred to fellowship with God through Christ.
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In the Old Testament God directed the nation of Israel to offer sacrifices of "covering for sin" (Leviticus 6:30; 16:20) or atonement.
These animal sacrifices could not take away sin. They could not really provide reconciliation with God (Hebrews 10:4).
But they foreshadowed the offering of God's Son as the perfect sacrifice. They were like a promisory note--to be paid one day by Christ (Romans 5:25)!
In the New Testament the Greek word (katallasso) often translated reconcile, doesn't just mean to cover sin or forgive it. It means to "change thoroughly from one position to another" (Ephesians 2:16, Colossians 1:20, 22).
We were sinners and "enemies" when Christ died for us.
8 But God demonstrates his own love for us in this: While we were still sinners, Christ died for us....if, while we were God’s enemies, we were reconciled to him through the death of his Son, how much more, having been reconciled, shall we be saved through his life! (Romans 5:8-10).
But now, as believers we are adopted into God's family!