by Matt Slick
Okay, so what the heck is the communicatio idiomatum, and why am I writing about it? The "uppity" sounding phrase is Latin for "communication of properties," and it is a very interesting and important doctrine. Let me explain.
Jesus has two natures: divine and human (John 1:1, 14, Phil. 2:5-8, Col. 2:9). He is at the same time one person with two natures. We call this the hypostatic union, that is, that in the one person of Jesus are two natures. This is important because it means that Jesus is the God-man, the One capable of dying for our sins and offering a sacrifice sufficient to the Father. The Communicatio Idiomatum (CI, for short) is important because it states that the attributes of both the divine and the human natures are each attributed/ascribed to the single person of Jesus. Here is an example.
In John 17:5, Jesus said, "And now, glorify Thou Me together with Thyself, Father, with the glory which I had with Thee before the world was." Now, Jesus the man did not exist until He was born on earth. So how is it that Jesus can then lay claim to the glory that He had "before He even existed as a man"? The answer is simple. The divine nature in Jesus has certain attributes such as omnipresence, omnipotence, eternality, etc. These attributes are ascribed to Jesus as the person. Therefore, Jesus could legitimately lay claim to the divine quality of eternal glory in relation to the Father. This whole thing becomes very important when we look at the cross.
When we sin, we offend an infinitely holy God. Therefore, our sin takes on a quality of an infinite offense. As finite sinners, we are not able do anything to please an infinitely holy God. Therefore, we need Jesus, who is God in flesh, to offer an infinitely valuable sacrifice on our behalf. The only way he can be infinitely valuable is if he is divine in nature. Got that?
However, when Jesus died on the cross, His divine nature did not die--only Jesus' human nature died. How then is Jesus' sacrifice infinitely sufficient to cleanse us if the divine nature did not die? Enter the communicatio idiomatum.
Since Jesus is one person with two natures (hypostatic union) and since the attributes of the two natures are ascribed to the one person, when Jesus died on the cross, His sacrifice was of infinite value because the qualities of divinity were ascribed to the one person of Jesus. Therefore, Jesus' sacrifice was infinite in value and capable of saving us from our sins even though it was only the human side of Christ that died.
This is why theology is so important. It unravels the hidden treasures of God's Word and discloses to us the wisdom and congruity of His wondrous truth. Furthermore, it brings glory to God through Christ as well as edifying the body of believers. We need to know and understand God's Word in all its intricacies so that we might be better able to know Him, speak His truth, and rest in His Son.