Can Christ be fully God and at the same time fully human? The validity and sufficiency of Christ’s sacrifice hinges upon the answer to this question. It is a mystery about the two natures of Christ, one that is quite baffling and, with our finite minds, cannot be fully comprehended.
The full divinity and the full humanity of Christ, also called the ‘hypostatic union,’ is essential to the credibility of man’s salvation. The doctrine of hypostatic union is our way of coming as close as we can to understanding Christ’s nature of being both God and man at the same time.
As to His full divinity, Jesus was God from the beginning (John 1:1-3, John 4:6, 19:28). He is co-existent, co-eternal, and co-equal with God the Father and God the Holy Spirit; He was involved in the creation of the universe and all living creatures. Biblically, there was no account of Jesus saying exactly, “I am Yahweh,” but he made statements in the Bible that pertain to His existence as a deity. One example was when He spoke to the Jews in John 8:58, “I tell you the truth, before Abraham was even born, I AM!” When He referred to Himself as “I AM,” instead of “I was”, He was using the same name that God used to introduce Himself to Moses and the Israelites in Exodus 3:14. This statement was either truth or blasphemy. The Jews were greatly appalled because they saw it as blasphemy, and were about to stone Jesus to death, but He escaped the mob.
Another instance of Jesus claiming His deity was when He claimed to be one with God the Father (John 10:30). When people worshipped Him, He never reprimanded them for it. Heavenly angels and God’s prophets would never accept worship, but Jesus did, which validates His claim as being fully God.
Throughout the world, we hear legends of characters being half-god and half-human, also known as demi-gods. Some examples in Greek mythology would be Hercules and Perseus, but Jesus cannot be likened to such myths. He is real and He is fully God, and fully man. His existence has undeniable evidence based on archaeological and historical proof. Ultimately, His full existence as a deity is what assures us of the sufficiency of His sacrifice on the cross to pay the eternal penalty of man’s sin. To say that He was just partly God is to degrade the absolute value of His sacrifice. The penalty of our offense against eternal God, which demands eternal death, can never be satisfied by any created being. The savior had to be God eternal. Jesus is fully God and He alone can pay and has already fully paid for our sins through His sacrifice on the cross.
As to the full humanity of Jesus, even though He was fully God and has always been that way, Jesus was made into flesh without diminishing or relinquishing His full divinity. This is also not fully comprehensible by the limited human mind. However, the concept of Him being fully God and fully human is a fact that is biblically established. According to John 1:1-3, 14:
“In the beginning was the Word, and the Word was with God, and the Word was God.  The same was in the beginning with God.  All things were made by him; and without him was not anything made that was made.  And the Word was made flesh, and dwelt among us, (and we beheld his glory, the glory as of the only begotten of the Father,) full of grace and truth.”
Many heresies in the past and in the modern age have surfaced to challenge the whole divinity and humanity of Christ. A few other notable ones were arianism, ebionism, and docetism. Such heretical teachings have aggressively challenged the doctrine of the hypostatic union. Arianism believes that Jesus is merely a created being. Docetism teaches that He is God, but not really human, while Ebionism holds that Jesus was merely human and was never God. Such heresies are fundamentally fallacious and unbiblical, in every way.
It is important to understand the importance of Jesus being fully human. The validity of His sacrifice to represent man leans upon His humanity. Romans 6:23 tells us that the payment for our sins is death, which means that man must shed his own blood to pay for his sins. Leviticus 17:11 states that our purification from sin and the way to make us right with God demands the shedding of blood. The law required the blood of animals as a substitute for human blood, but we find in Hebrews 10:3-5 that animal blood is not enough and cannot take away our sins.
(Hebrews 10:3-5 KJV)
3 But in those sacrifices there is a remembrance again made of sins every year.
4 For it is not possible that the blood of bulls and of goats should take away sins.
5 Wherefore when he cometh into the world, he saith, Sacrifice and offering thou wouldest not, but a body hast thou prepared me:
Thus, Christ must have fully human blood to completely represent man in His sacrifice. So, does this mean that any human can be a sacrifice for all humanity? You see, just as the temporary animal sacrifice had to be unblemished, so too does the ultimate human sacrifice have to be a perfect human. Only Jesus lived a sinless life; therefore, only His human blood can completely satisfy the penalty of our sins.
(2 Corinthians 5:21 KJV)
For he hath made him to be sin for us, who knew no sin; that we might be made the righteousness of God in him.
Lastly, Jesus Christ’s humanity allows Him to relate with man. When He was born here on earth and lived with us, He experienced human suffering, temptation, and even death. Hebrews 4:15-16 tells us that Jesus is our High Priest, who understands our weaknesses, for he faced all of the same tests that we do, yet he did not sin. Because of this, we can boldly approach God’s throne of grace to receive mercy, and find grace to help us when we need it most.
Jesus, the eternal Son of God, is the ultimate sacrificial lamb of God that took away all our sins by shedding His human blood on the cross. This free gift given to us through Jesus Christ is available for everyone who asks. We don’t have to be perfect to approach God and receive forgiveness and reconciliation. Jesus lived a perfect life that we could never live and died as a perfect sacrifice to pay for all our sins. You simply need to approach that throne of grace, accept His sacrifice, and receive Him as your Lord and Savior. God’s love is unconditional, evidenced by the fact that He went through so much trouble and pain for our eternal salvation.