Q: What sort of Redeemer is needed to bring us back to God?
ANSWER: One who is truly human and also truly God.
One of the more difficult doctrines of orthodox Christianity is what theologians term the "hypostatic union," which describes the personal union of Jesus' human and divine natures. The term "hypostasis" is a transliteration of the Greek word ὑπόστασις, translated as "nature" in the letter to the Hebrews: "He is the radiance of the glory of God and the exact imprint of his nature, and He upholds the universe by the word of His power. After making purification for sins, He sat down at the right hand of the Majesty on high."
The doctrine of the hypostatic union resists all attempts to argue that Christ is only partly human, and therefore not fully subject to the human condition, or only partly divine, and therefore not of one being with the Father. Rather, He is both truly and fully human and simultaneously truly and fully God. He is fully human, in that he endured all of the hardship and temptations that we humans encounter, yet he did so without sin, holy and innocent. He is fully God, being present at the beginning with God, and Himself being God. Jesus Christ is the true God-man. And only such a Person could achieve our redemption, for it is the unity of these two natures in Jesus that makes Him the only possible Redeemer for our sins and the only possible mediator between God and men.
For to us a child is born, to us a son is given; and the government shall be upon his shoulder, and his name shall be called Wonderful Counselor, Mighty God, Everlasting Father, Prince of Peace.
In the beginning was the Word, and the Word was with God, and the Word was God.