Why was it necessary that our Redeemer be divine? Of course, we must have a substitute to bear our punishment in our place. But wouldn’t a merely sinless human do? Was it necessary that God must come down to earth? Dr J. Ligon Duncan, a Presbyterian Pastor and Scholar, provides some helpful points on this. The full article can be found here.

The Westminster Larger Catechism asks in Question 38: “Why was it requisite that the Mediator should be God?” It wisely and biblically answers:

It was requisite that the Mediator should be God, that he might sustain and keep the human nature from sinking under the infinite wrath of God, and the power of death; give worth and efficacy to his sufferings, obedience and intercession; and so satisfy God’s justice, procure his favour, purchase a peculiar people, give his spirit to them; conquer all their enemies, and bring them to everlasting salvation (Acts 2:24–25; Rom. 1:4; Acts 20:28; Heb. 9:14; Heb. 7:25–28; Rom. 3:24–26; Eph. 1:6; Matt. 3:17; Titus 2:13–14; Gal. 4:6; John 15:26; Luke 1:68–69, 71, 74; Heb. 5:8–9; Heb. 9:11–15).

Herein we may detect at least eight theological reasons for the indispensability of the deity of our Lord.

(1) Christ’s divinity was necessary to bear the force of the atonement. The weight of the wrath of God, for the sins of the world, is so great that no mere mortal could have borne it. It was Christ’s lot to drink that cup to its bitter dregs. Only a divine Savior could have survived it.

(2) Christ’s divinity was necessary to imbue his mediatorial labors with limitless value. An almost infinite satisfaction was due God in view of the sins of humanity. No finite being could pay such a price and thus answer the full requirements of strict covenantal justice.

(3) Christ’s divinity was necessary to quit God’s punitive wrath. The covenant of works required perfect and personal obedience, upon penalty of death. The consequent defection of Adam and Eve from their covenantal obligation plunged the whole race into an age-long rebellion against God. Only the Father’s costly sacrifice of his beloved only begotten Son was adequate to fulfill the just sentence due us all from the Almighty.

(4) Christ’s divinity was necessary to secure the Father’s favor. Not because God had to be forced or coaxed to love his people. Not at all. Indeed, the atonement did not “make” God love us, but rather is the expression of his love and indispensable condition of his covenantal favor towards us. Nevertheless, once God set his love on us to redeem us, and infinite penalty and positive righteousness was required to secure his eternal benediction. Such an accomplishment required the divine Savior.

(5) Christ’s divinity was necessary to redeem a people for himself. The divine Christ literally purchased his people Christ earned our salvation. We are saved by works: his works! Only a divine savior could have paid the costly purchase price for redeeming us from our bondage to sin and death.

(6) Christ’s divinity was necessary for the pouring out of the Spirit on his people. It was essential that our salvation be both accomplished and applied. Christ told his disciples that it was necessary that he ascend to the right hand of the Father in order to send the Holy Spirit (Jn 16:7). Only the eternal God-man holds the right to send the Spirit where he will, that his salvation might be applied to all his people.

(7) Christ’s divinity was necessary for the conquest of all his people’s enemies. Our Lord, the Captain of our Salvation, not only made satisfaction for the condemning power of sin, but also decisively destroyed the might of Satan, the world, and death. This destructive work of redemption required the infinite capacities of the divine Captain of the Hosts of the Lord.

(8) Christ’s divinity was necessary to accomplish our everlasting salvation. Our eternal blessedness essentially consists in the enjoyment of our Savior. He is not only the author of our redemption, he is the matter of it. He is not merely the means of our salvation, he is the goal of it. In glory we are not only made happy by him, but in him. Only a divine savior could serve as the great fountain of blessedness for all redeemed humanity.