It would be wrong to think that Christ's two natures mix together to form a third kind of nature. This is one of the heresies that the early church had to combat. This heresy taught that "the human nature of Christ was taken up and absorbed into the divine nature, so that both natures were changed somewhat and a third kind of nature resulted. An analogy to [this] can be seen if we put a drop of ink in a glass of water: the mixture resulting is neither pure ink nor pure water, but some kind of third substance, a mixture of the two in which both the ink and the water are changed. Similarly, this view taught that Jesus was a mixture of divine and human elements in which both were somewhat modified to form one new nature. This view is unbiblical because it demolishes both Christ's deity and humanity. If Christ's two natures mixed together, then He is no longer truly and fully God and truly and fully man, but is some entirely different kind of being that resulted from a mixture of the two natures.
But, even if we acknowledge that the natures do not mix together into a third kind of nature, it would also be wrong to think that the two natures changed one another. For example, it would be wrong to conclude that Jesus' human nature became divine in some ways, or that His divine nature became human in some ways. Rather, each nature remains distinct, and thereby retains its own individual properties and does not change. As the council of Chalcedon stated it,
"...the distinction of natures being by no means taken away by the union, but rather the property of each nature being preserved..."
Jesus' human nature is human, and human only. His divine nature is divine, and divine only. For example, Jesus' human nature did not become all knowing through its union with God the Son, and neither did His divine nature become ignorant of anything. If any of the natures underwent a change in its essential nature, then Christ is no longer truly and fully human, or truly and fully divine.
Christ is only one Person
What we have seen so far about the deity and humanity of Christ shows us that Christ has two natures -- a divine nature and a human nature -- and that each nature is full and complete, that they remain distinct and do not mix together to form a third kind of nature. But if Christ has two natures, does this mean that He is also two people? No, it does not. Christ remains one Person. There is only one Christ. The church has historically stated this truth in this way: Christ is two natures united in one person forever.
At this point we encounter another heretical view to beware of. This view, while acknowledging that Jesus is fully God and fully man, denies that He is only one Person. According to this view, there are two separate persons in Christ as well as two natures. In contrast to this, the Bible is very clear that, while Jesus has two natures, He is only one Person. In other words, what this means is that there are not two Jesus Christ's. In spite of the fact that He has a duality of natures, He is not two Christs, but One. While remaining distinct, the two natures are united together in such a way so as to be one Person.
Put simply, there is a certain sense in which Christ is two, and a different sense in which Christ is one. He is two in that He has two real, full natures one divine and one human. He is one in that, while remaining distinct, these two natures exist together in such a way as that they constitute "one being." In other words, the two natures are both the same Jesus, and thus are one Person. Again, as the Chalcedonean creed says, Christ is ...
"to be acknowledged in two natures...concurring in one Person and one Subsistence, not parted or divided into two persons, but one and the same Son, and only begotten, God, the Word, the Lord Jesus Christ..."
Things that are true of one nature but not the other are nonetheless true of the Person of Christ. The fact that Christ is two natures means that there are things that are true of His human nature that are not true of His divine nature. And there are things true of His divine nature that are not true of His human nature. For example, His human nature hungered, but His divine nature could never be hungry. So when Christ hungered on earth, it was His humanity that hungered, not His divine nature.
By virtue of the union of the natures in one Person, the things that are true of and done by only one of Christ's natures, are nonetheless true of and done by the Person of Christ. In other words, things which only one nature does can be considered to have been done by Christ Himself. Likewise, things that are true of one nature but not the other are true of the Person of Christ as a whole. What this means, in simple terms, is that if there is something that only one of Christ's natures did, He can still say, "I did it."
We have many instances in Scripture which demonstrate this. For example, Jesus says in John 8:58, "...before Abraham was born, I am." Now, Christ's human nature did not exist before Abraham. It is Christ's divine nature that eternally exists before Abraham. But since Christ is one Person, He could say that before Abraham was, He is. Another example is Christ's death. God cannot die. We should never speak of Christ's death as the death of God. But humans can die, and Jesus' human nature did die. Thus, even though Jesus' divine nature did not die, we can still say that the Person of Christ experienced death because of the union of the two natures in the one Person of Christ. Because of this, Grudem says, "by virtue of union with Jesus' human nature, his divine nature somehow tasted something of what it was like to go through death. The person of Christ experienced death."
How could Jesus say that He did not know the day or hour of His return (Matthew 24:36) even though He is omniscient (John 21:17). If Jesus is God, why didn't He know the day of His return? This is solved by our understanding that Christ is one Person with two natures. The answer is that in regards to His human nature, Jesus does not have all knowledge. Thus, in His human nature He really did not know the day or hour of His return. But in His divine nature, He does have all knowledge and thus in His divine nature He did know when He would return.
(Continued in Part 3 here)