Institutes of the Christian Religion (1559) - John Calvin
Book 2 - God the Redeemer
Chapter 12 - Christ had to become Man in Order to Fulfill the Office of Mediator
Sections 4-7 - Objections answered
Section 4 - The sole purpose of Christ's incarnation was our redemption
It's useless to speculate if He would have become man, if we didn't sin.
He came to expiate sin - Heb 9:11-12, 22; Isa 53:4-6.
To move us from death to life - John 1:9-11, 14; 3:16; 5:25; 11:25; Matt 18:11; 9:12.
To reconcile us to God - Heb 5:1; 2 Cor 5:19; Rom 8:3-4; Titus 2:11; Luke 24:46-47; John 10:15-18; John 3:14; 12:23, 27-28; Luke 1:79.
Section 5 - Would Christ have also become man if Adam had not sinned?
Eph 1:4-6 shows that God meant His Son to redeem us before the world began.
We should remain in Christ, and not try to speculate beyond Him.
Eph 3:14-19; 1 Tim 1:15; 2 Tim 1:9.
Section 6 - Osiander's doctrine of the image of God
This error comes from thinking our being - body and soul - is patterned after what Messiah would be. But the angels also bear God's image, so did Messiah have to be like them, too? No. The image of God in us is that which sets us apart from the animals.
Section 7 - Point by point refutation of Osiander
Jesus would not have to become man, were there no Fall.
Jesus didn't have to be the first man, physically. He was made like us - Heb 4:15 - a descendant of Adam - Luke 3:38 - the second Adam - 1 Cor 15:47.
Jesus was still head of the human race, as the exact image of God, surpassing angels and men, also in the image of God - Col 1:14-16, 18.
Christ could rule angels and men without becoming man.
Osiander misapplies Gen 2:23, thinking God spoke it to Christ first, of the church. This is nonsense.
Gal 4:4-5 clinches it: Jesus was born of a woman to redeem mankind.