Both Sacred Scripture and Sacred Tradition teach that Jesus Christ died specifically for the expiation of our sins. Historical Christianity professes that God became a man by way of Incarnation to restore man's fallen nature to full communion with the Godhead.
Consequently, just as one trespass resulted in condemnation for all people, so also one righteous act resulted in justification and life for all people. (Romans 5:18)
For God so loved the world, that He gave His only begotten Son, that whoever believes in Him shall not perish, but have eternal life."For God did not send the Son into the world to judge the world, but that the world might be saved through Him.… (John 3:16)
The Nicene-Constantinopalitan Creed professes:
...for us men, and for our salvation, came down from heaven, and was incarnate by the Holy Ghost of the Virgin Mary, and was made man..
The current Catholic Catechism states about man's specific responsibility for "nailing" Jesus to the Cross with our sin:
All sinners were the authors of Christ's Passion
Paragraph 598 In her Magisterial teaching of the faith and in the witness of her saints, the Church has never forgotten that "sinners were the authors and the ministers of all the sufferings that the divine Redeemer endured." Taking into account the fact that our sins affect Christ himself, the Church does not hesitate to impute to Christians the gravest responsibility for the torments inflicted upon Jesus, a responsibility with which they have all too often burdened the Jews alone:
We must regard as guilty all those who continue to relapse into their sins. Since our sins made the Lord Christ suffer the torment of the cross, those who plunge themselves into disorders and crimes crucify the Son of God anew in their hearts (for he is in them) and hold him up to contempt. And it can be seen that our crime in this case is greater in us than in the Jews. As for them, according to the witness of the Apostle, "None of the rulers of this age understood this; for if they had, they would not have crucified the Lord of glory." We, however, profess to know him. And when we deny him by our deeds, we in some way seem to lay violent hands on him.(1)
Nor did demons crucify him; it is you who have crucified him and crucify him still, when you delight in your vices and sins.(2)
- Roman Catechism I, 5, 11; cf. Heb 6:6; 1 Cor 2:8.
- St. Francis of Assisi, Admonitio 5, 3.
The Church also teaches that God gave man free will...beginning with Adam.
Paragraph 1730 God created man a rational being, conferring on him the dignity of a person who can initiate and control his own actions. "God willed that man should be 'left in the hand of his own counsel,' so that he might of his own accord seek his Creator and freely attain his full and blessed perfection by cleaving to him."(1)
Man is rational and therefore like God; he is created with free will and is master over his acts.(2)
MAN'S FIRST SIN
Paragraph 397 Man, tempted by the devil, let his trust in his Creator die in his heart and, abusing his freedom, disobeyed God's command. This is what man's first sin consisted of.(3) All subsequent sin would be disobedience toward God and lack of trust in his goodness.
Paragraph 398 In that sin man preferred himself to God and by that very act scorned him. He chose himself over and against God, against the requirements of his creaturely status and therefore against his own good. Constituted in a state of holiness, man was destined to be fully "divinized" by God in glory. Seduced by the devil, he wanted to "be like God", but "without God, before God, and not in accordance with God".(4)
- GS 17; Sir 15:14.
- St. Irenaeus, Adv. haeres. 4,4,3:PG 7/1,983.
- Cf. Gen 3:1-11; Rom 5:19.
- St. Maximus the Confessor, Ambigua: PG 91,1156C; cf. Gen 3:5.
However, paradoxically speaking...
Scripture also explicitly teaches that Jesus Christ is God - who is omnipotent, omniscient, and omnipresent.
In the beginning was the Word, and the Word was with God, and the Word was God. He was with God in the beginning. (John 1:1-2)
Jesus Christ is the same yesterday and today and forever. (Hebrews 13:8)
The Miaphysite heresy - which holds that the human nature and pre-incarnate divine nature of Christ were united as one divine human nature from the point of the Incarnation onward - was officially denounced at the Council of Chalcedon.
The Confession of Chalcedon provides a clear statement on the human and divine nature of Christ:
We, then, following the holy Fathers, all with one consent, teach people to confess one and the same Son, our Lord Jesus Christ, the same perfect in Godhead and also perfect in manhood; truly God and truly man, of a reasonable [rational] soul and body; consubstantial [co-essential] with the Father according to the Godhead, and consubstantial with us according to the Manhood; in all things like unto us, without sin; begotten before all ages of the Father according to the Godhead, and in these latter days, for us and for our salvation, born of the Virgin Mary, the Mother of God, according to the Manhood; one and the same Christ, Son, Lord, only begotten, to be acknowledged in two natures, inconfusedly, unchangeably, indivisibly, inseparably; (ν δύο φύσεσιν συγχύτως, τρέπτως, διαιρέτως, χωρίστως – in duabus naturis inconfuse, immutabiliter, indivise, inseparabiliter) the distinction of natures being by no means taken away by the union, but rather the property of each nature being preserved, and concurring in one Person (prosopon) and one Subsistence (hypostasis), not parted or divided into two persons, but one and the same Son, and only begotten God (μονογεν Θεόν), the Word, the Lord Jesus Christ; as the prophets from the beginning [have declared] concerning Him, and the Lord Jesus Christ Himself has taught us, and the Creed of the holy Fathers has handed down to us.
Considering all this...it seems to me that, although the Incarnation is a temporally necessary for Man's salvation, it ultimately is eternal in essence since the essence of God eternally transcends time.
If Adam, by exercising his free will, had chosen not to partake of the forbidden fruit (a.k.a. Original Sin), would the Incarnation still have taken place due to God's omnipresence?
I'm looking for authoritative Catholic/Orthodox teaching about this subject.