Why is the full and complete humanity of the Son of God incarnate so vital to the Christian faith? H.R. Mackintosh helpfully responds in summary form:
The true manhood of Jesus is of cardinal significance in four ways.
(1) It guarantees a veritable incarnation. If the manhood of Christ is unreal, at any remotest point, God has not quite stooped to unity with man. He has not come so low as we require; there has been reservation and refusal; some part of our burden, after all, has been left untouched. ” The unassumed is the unhealed.” In that case, no matter from what height Christ came, He has not reached to us, but has stopped short…. But it has not been so. The centre of the catholic faith is that God in Christ came the whole way: “forasmuch as the children were sharers in flesh and blood, He also in like manner partook of the same.” He drew near in person, that we might clasp Him as a kinsman in our arms, and feel the Infinite One to be our own. This has touched men most, breaking the world’s hard heart. The measure of Jesus’ humanity
is the measure of God’s love. As it has been put, “love is not in full possession until it can fully display itself”; and as Christ passed from depth to depth, entering one chamber after another of human experience, and submitting at length to death itself, He gave a proof of Divine love than which nothing greater can be conceived….
(2) It provides an essential basis of atonement. All true Christian ideas in regard to atonement may be viewed as aspects of Jesus’ self-identification with the sinful. If then He who lived and died for men had Himself been man only in seeming, or in part, no expiation were after all made in our name; for only He can act with God for man who speaks from man’s side. It is as Christ became our fellow, moving in a true manhood through obedience, conflict, and death, that He entered into our condition fully and availed in our behalf to receive from God’s hand the suffering in which is expressed the Divine judgment upon sin. Jesus’ manhood is the corner-stone of reconciliation.
(3) It secures the reality of a perfect example. Jesus is our pattern in faith and prayer; but it cannot be too clearly understood that no act can be exemplary which is not first of all dutiful. The human Christ prayed, not in order that He might furnish a model to His disciples, but because to Him prayer was an inward need and duty. So profound and unmanning was His fear in Gethsemane that like the children of men He took refuge under God’s shadow, and was heard for His reverent trust. In our temptations it is everything to know that He also was tempted. And here that sinless manhood, which has seemed at times to remove Him from us, and to make sympathy impossible, reveals itself as the nerve and spring of His redemptive power. It is not, one may surmise, to those who themselves once fell in drunkenness or lust that frail men and women instinctively look for aid and hope; it is rather to those who, although schooled in fellow-feeling by temptation, have kept their virtue pure. So Jesus’ victory constitutes Him the source of victory for men; in Him, if we may put it so, Divine grace is humanised, and made available for sinners….
(4) It points to our eternal destiny. It is because Jesus the Man has risen from the grave and passed to a transcendent life with God that we too may triumph in prospect over death. As St. Paul has expressed it, with his most delicate precision in the use of our Lord’s names, “if we believe that Jesus died and rose again, even so them also which sleep in Jesus shall God bring with Him.” For the resurrection of Jesus, our human Surety and Comrade, is a test case; and as such it has fixed a principle, revealing as it does how the Father’s love and power will deal with all believers. Thus once more the central significance of Christ’s true humanity is manifest. On its integrity and perfect wholeness rest for us the unspeakable consolations of faith in a blessed immortality.
from The Doctrine of the Person of Jesus Christ (New York: Charles Scribner’s Sons, 1912), 404-406.