What does it mean that Christ reconciled the world? And why?
The doctrine of salvation is rooted in creation. We must know what man is or was in order to understand salvation. The essential understanding is that man was restored from the fall. Restored to fulfill the created purpose of man's existence, to be eternally in union with God.
One of the most basic underlying premises of scripture is that man was created free. That he possesses a rational soul, free from coercion.
Created in His image entails freedom, uniqueness, and is relational. There is no necessity for God to create. He did it at His good pleasure. Man was also called to grow into the likeness of God. It has a dynamism, it is not static. This is confirmed by Paul in Rom 8:29 and Gal 4:19.
As II Pet 1:4 states, we were created to share in the Divine Nature. The redemption of mankind is to restore man's ability and capability to become by grace, to be transformed into the likeness of God. Whether we fulfill our human vocation and live according to God's image or whether we reject God is up to each of us.
This growing into His likeness, being conformed to His Image, being the Mind of Christ, to be perfect as He is perfect, to be partakers of His Divine Nature, this is known as Theosis. This was the created purpose of man. We were created in order to do the works created for us. To bring ourselves and creation back to God as a living sacrifice so that God could be all in all. This is also referred to as salvation, the salvation of individual man. Salvation is the goal, the confirmation of our created purpose.
However, the fall separated man from God. We fell from this lofty abode of having a mutual, loving, obedient, relationship with God. In order to restore this communion and union, Christ needed to restore mankind and creation to the status it was before the fall. Man was unable to restore himself. He could not bring life back from a dead position (being mortal). Thus Christ was Incarnated, took on our fallen human nature in order to redeem that nature, to restore it, reconcile it back to God, so God could once again enter into a communal relationship with His creature, man. Col 1:15-20.
Though man disobeyed and fell, God also provided redemption. God was not willing to allow His creation to simply dissolve back into nothingness after the fall. The Revelation we have in the OT is God's message and the preparation of the coming of the Messiah. God sent His Only Son, Christ, to reconcile the world unto himself, II Cor 5:14-19. Because Christ is the eternal image of the Father, He alone is able to renew the image of God in man. Col 1:15-20; John 5:28-29; Rom 5:12, Rom 5:14-19; Rom 11:32; Rom 8:20, I Cor 15:12-22; II Tim 1:10, Heb 2:9 Heb 2:14-17, Col 1:20, I John 2:2, John 1:29, John 6:39. Texts that corroborate this view are: Acts 24:15; Acts 23:6; I Cor 15:52, Eph 1:10; Eph 2:1-5, John 5:28, John 12: 32, I Tim 4:10, Is 26:19, Dan 12:2, Luke 2:30-32, Rev 20:12-13. They also show the universality of Christ's redemptive work. John 4:42, I John 4:14.
Christ's work on the Cross is solely Grace, man has nothing to do with it, it is totally objective. See: John 1:13, I Pet 1:23, James 1:18, Gal 4:4, Heb 2:11, Rom 9:16.
Christ came to us Incarnate. Heb 2:14, I John 3:8, John 1:14, I John 3:8. Meaning He was both God and Man. It means that the joining of God's perfect Image was to be reunited with the fallen image of man and creation. Thus in summation, man lost the perfect created image in which he was made and lost the ability to commune with God so that man could attain Godlikeness. He lost life.
The Incarnation of our human nature was a necessity in order that Christ could redeem it. Christ became man, consubstantial with man, in order to effect the changes necessary to redeem our natures. Adam's sin resulted in a judgment against man's nature, death. Man became mortal, living in a state of death. Thus all men are born dead, by nature, inherited corruptness. It is from this state of death, mortality, the flesh that sin originates in man I Cor 15:56..
Salvation is the restoration of God's image in man, the uniqueness of each one of us, and our personhood, that of being relational. Christ in His death restored our nature. By His Life we live - we are able to fulfill our personhood. He overcame Death, freed mankind from the bondage to death and sin so that we could have communion again with Him. Mankind is saved from the fall so that man could freely choose to work with God as a created creature which is also called the salvation of one's soul or attaining eternal life.