Reconciliation is mainly a New Testament concept.  It is the change for the better a relationship between two or more persons.  Theologically it refers to the change of the relationship between God and man. We are naturally children of wrath (Eph. 2:3) and are at enmity with God (Eph. 2:11-15), but, ” . . . we were reconciled to God through the death of His Son . . . ”  (Rom. 5:10). Because of the death of Jesus, the Christian’s relationship with God is changed for the better. We are now able to have fellowship with Him (1 John 1:3) whereas before we could not. So, we are reconciled to Him (Rom. 5:10-11). The problem of sin that separates us from God (Isaiah 59:2) has been addressed and removed in the cross. It was accomplished by God in Christ (2 Cor. 5:18).

Reconciliation is advocated in Scripture.

• Matthew 5:23–24, “Therefore if you are presenting your offering at the altar, and there remember that your brother has something against you, 24 leave your offering there before the altar and go; first be reconciled to your brother, and then come and present your offering.”
• 2 Corinthians 5:18–19, “Now all these things are from God, who reconciled us to Himself through Christ and gave us the ministry of reconciliation, 19 namely, that God was in Christ reconciling the world to Himself, not counting their trespasses against them, and He has committed to us the word of reconciliation.”
• Ephesians 2:13–14, “But now in Christ Jesus, you who formerly were far off have been brought near by the blood of Christ. 14 For He Himself is our peace, who made both groups into one and broke down the barrier of the dividing wall,”